15-Amp vs. 20-Amp Outlets: How to Tell Which One Your Circuit Needs

Quick answer

The circuit decides which wall outlet you need, not the appliance you plan to plug in. Find the breaker that feeds the box, confirm the conductor size, then read the outlet face as a cross-check. A 15-amp breaker on 14 AWG copper is a 15-amp branch; a 20-amp breaker on 12 AWG copper is a 20-amp branch ^[1][4].

The code sets the permitted pairings in Table 210.21(B)(3): a 20-amp branch accepts either a 15-amp or a 20-amp receptacle, while a 15-amp branch accepts only a 15-amp receptacle ^[2]. And before you buy anything, know that replacing a receptacle triggers its own set of current-code requirements under 406.4(D) — GFCI, AFCI, and tamper-resistant protection can all be mandatory on the replacement even when the original device predated them ^[5].

One caution before you shop. If the breaker and the conductor disagree with each other, what you have found is a wiring defect rather than a receptacle to match, and that belongs with a licensed electrician instead of a shopping list.

The key points:

• Two independent checks, and they have to agree. The breaker tells you what the circuit is protected at. The conductor tells you what the circuit is allowed to be protected at — 240.4(D) caps 14 AWG copper at 15 amperes and 12 AWG copper at 20 amperes ^[4]. If the two disagree, you have found a wiring problem, not an outlet question.
• The direction of the mismatch matters. A 15-amp receptacle on a 20-amp branch is permitted and common. A 20-amp receptacle on a 15-amp branch is not permitted ^[2]. The T-shaped slot is not a free upgrade.
• A 20-amp face is strong evidence; a 15-amp face is weak evidence. Because Table 210.21(B)(3) allows 15-amp receptacles on 20-amp circuits, a plain face tells you very little about the branch behind it ^[2].
• One receptacle alone on its own circuit follows a stricter rule. Under 210.21(B)(1), a single receptacle on an individual branch circuit must be rated no less than the circuit itself ^[2]. So a lone 15-amp receptacle on a dedicated 20-amp circuit is a violation, even though a duplex on a shared 20-amp circuit is fine ^[3].
• Replacement is not a like-for-like right. 406.4(D) requires the replacement to meet today's rules for that location, which is where GFCI, AFCI, and tamper resistance enter a job that looked like a simple swap ^[5][6][8][9].
• Some rooms are already settled by code. Kitchen small-appliance, laundry, and bathroom receptacle circuits are required to be 20 amperes ^[7]. In those spaces the question is often not "which is it" but "why is this one different than it should be."

The two ratings, and why the face is only half the story

Two words get used loosely in this topic. Strictly, a receptacle is the device — the part with slots that you screw into the box. An outlet is the point in the wiring system where power is taken, which is why the Code's own term for the location is "receptacle outlet."

In everyday shopping language the two are interchangeable. A listing for a 15 amp duplex outlet, a 15A duplex receptacle, and a standard electrical outlet on a 15-amp branch all describe the same part. This guide follows that everyday usage where nothing turns on it, and switches to the precise sense when quoting a code requirement.

One definition does matter: a duplex receptacle has two contact devices on one yoke, which means a single duplex outlet counts as two receptacles for code purposes ^[2]. That detail decides a rule later in this article.

Both 15-amp and 20-amp residential receptacles run at the same nominal 120 volts, so voltage is not what separates them. Every standard electrical outlet in a US dwelling is a 120-volt device. What differs is the ampere rating of the branch circuit and the receptacle configuration that belongs on it.

The configurations themselves are dimensional standards, defined in NEMA WD 6 ^[10] and evaluated for safety under UL 498 ^[11]:

The asymmetry between those two rows is the single most useful thing to understand here. A T-slot is close to proof; a plain face is barely a hint. Most guides treat the face as the answer, and that is exactly backwards for the more common case.

Before opening any device, shut off the breaker and verify the receptacle is de-energized with a tester. Treat that as non-negotiable rather than a formality — the rest of this article assumes it.

Start at the breaker: the circuit rating is the decision

Go to the panel first. The overcurrent device is what defines the branch-circuit rating: a breaker marked 15 is protecting a 15-amp branch, a breaker marked 20 is protecting a 20-amp branch.

The existing receptacle cannot substitute for this. Houses get remodeled, devices get swapped by previous owners, and panel directories go stale. What has been in the wall for twenty years is evidence of what someone once installed, not of what the circuit is rated for.

Panel labeling still helps, even when it is imperfect. A directory entry reading "Kitchen Small Appliance," "Laundry," or "Bathroom" points at a circuit that 210.11(C) already requires to be 20 amperes ^[7]. An entry reading "Bedroom outlets" or "Living room" more often indicates a 15-amp branch, though that is a tendency rather than a rule.

One practical caution: a single breaker frequently feeds more than one room. A bedroom receptacle may share a branch with part of a hallway; a home office may be tied into an adjacent space. That matters because everything on the branch shares the same rating, so identifying the breaker also means identifying everything else it serves.

Wire gauge: the code limit that makes the breaker meaningful

The breaker tells you how the circuit is protected. The conductor tells you how it is allowed to be protected, and that limit is fixed rather than a rule of thumb.

NEC 240.4(D) caps overcurrent protection for small conductors regardless of what an ampacity table would otherwise allow: 14 AWG copper is limited to 15 amperes, 12 AWG copper to 20 amperes, and 10 AWG copper to 30 amperes ^[4]. Aluminum is more restrictive — 12 AWG aluminum is limited to 15 amperes ^[4]. These values do not get the benefit of rounding up to the next standard breaker size.

So the two checks resolve to a short table:

With the power off and the device pulled forward, the cable jacket or conductor insulation normally carries printed size markings. What you want is agreement: 15-amp breaker with 14 AWG copper, or 20-amp breaker with 12 AWG copper.

Disagreement is the finding that changes the job. A 20-amp breaker on 14 AWG copper exceeds the 240.4(D) limit and is a wiring defect to correct, not a receptacle to match ^[4]. Remodeled homes are where this shows up most: one segment of a run is newer than another, or a previous installer changed the device without touching the branch wiring. Checking one clue is how that goes unnoticed.

Reading the face: NEMA 5-15R and 5-20R

Once the breaker and conductor agree, the face becomes a confirmation step rather than the decision.

A NEMA 5-15R has two straight vertical slots. A NEMA 5-20R has one T-shaped neutral slot, which is what lets it accept a 20-amp plug in addition to a standard one ^[10]. The shape is a mechanical interlock, not styling: it exists so a 20-amp plug physically cannot enter a 15-amp receptacle.

Read the result asymmetrically:

• Found a 5-20R? The branch is almost certainly 20 amperes, because installing one on a 15-amp circuit is not permitted ^[2]. Confirm at the panel anyway.
• Found a 5-15R? You have learned almost nothing about the branch. It is permitted on 15- and 20-amp circuits alike ^[2]. The breaker and conductor decide.

Many devices also carry their rating stamped or molded on the strap or body. That marking describes the device, not the circuit.

What the code permits in each direction

A clear answer earns its keep here, because the two directions are not symmetrical.

Table 210.21(B)(3) sets the permitted receptacle rating for a branch circuit supplying two or more receptacles ^[2]:

A 15-amp receptacle on a 20-amp branch is permitted. It is also extremely common in existing homes, and it is not a defect. Part of why it works sits on the product-standard side: receptacles are evaluated under UL 498, and that evaluation tests the side and rear terminals concurrently rather than one wiring path at a time ^[11]. A 15-amp duplex wired feed-through on a 20-amp circuit is therefore assessed with current passing through its terminals, not only with current drawn from its own face.

A 20-amp receptacle on a 15-amp branch is not permitted. The reason is the table, not aesthetics or misrepresentation: on a 15-amp circuit the permitted receptacle rating is 15 amperes ^[2]. A T-slot on a 15-amp branch advertises a 20-amp capability the circuit cannot deliver, and the conductor behind it is limited to 15 amperes by 240.4(D) ^[4].

The single-receptacle case is stricter, and it is the exception people miss. Under 210.21(B)(1), a single receptacle installed on an individual branch circuit must have an ampere rating not less than the branch-circuit rating ^[2][3]. A duplex is two receptacles, so it does not fall under this rule ^[2] — but a true single receptacle on a dedicated 20-amp circuit must be rated 20 amperes. This is the situation on dedicated appliance circuits, and it reverses the usual "15 on 20 is fine" guidance.

The rule most replacement guides leave out: 406.4(D)

Here is the part that turns replacing a wall outlet from a routine swap into a code question, and it is missing from most articles on this topic.

NEC 406.4(D) states that replacement of receptacles shall comply with 406.4(D)(1) through (D)(8), as applicable ^[5]. In plain terms: when you replace a receptacle, the replacement has to satisfy today's requirements for that location — not the requirements that applied when the house was built. The relevant provisions for a residential swap:

Two consequences worth stating plainly.

A tamper resistant outlet is a requirement on replacements, not a feature to shop for. Where 406.12 requires tamper-resistant receptacles, 406.4(D)(5) requires the replacement to be a listed tamper-resistant device ^[5][6]. So when a product is described as a tamper resistant duplex receptacle, that shutter mechanism is satisfying a code obligation in covered locations rather than adding an optional safeguard. Treating it as a nice-to-have is a common framing error in shopping guides.

AFCI and GFCI are different devices for different hazards, and both can apply. A ground-fault circuit interrupter compares current leaving on the hot conductor with current returning on the neutral and opens the circuit when they no longer balance — it is shock protection for people, required by location under 210.8 ^[8]. An arc-fault circuit interrupter detects the electrical signature of arcing and opens the circuit before that arc can start a fire — it is fire protection for the wiring, required by circuit type under 210.12 ^[1]. They are not substitutes, which is why 406.4(D)(2) and 406.4(D)(4) are separate provisions ^[5]. Some replacement devices are dual-function and provide both.

Whichever applies, the device has to be reachable. The code requires arc-fault and ground-fault circuit-interrupter type receptacles to be installed in a readily accessible location ^[5]. A GFCI buried behind a refrigerator does not satisfy that.

Because GFCI and AFCI requirements are location-specific and have shifted across recent code editions, the applicable edition matters. Jurisdictions adopt the NEC on their own schedules and amend it, so the version enforced where you live is a local question ^[1].

Room by room: where the code already requires 20 amperes

Room type is usually described as a soft clue. For three cases it is not a clue at all — the code names the circuit rating directly in 210.11(C) ^[7]:

• Kitchen and dining areas — 210.11(C)(1). Two or more 20-ampere small-appliance branch circuits are required for the receptacle outlets specified in 210.52(B), covering the kitchen, pantry, breakfast room, dining room, and similar dining areas ^[7].
• Laundry — 210.11(C)(2). At least one additional 20-ampere branch circuit is required for laundry receptacle outlets ^[7].
• Bathrooms — 210.11(C)(3). At least one 120-volt, 20-ampere branch circuit is required to supply bathroom receptacle outlets, and that circuit is not permitted to serve other outlets ^[7].

All three circuit types are also restricted in what else they may feed: small-appliance, laundry, and bathroom branch circuits are permitted to supply only the receptacle outlets specified in their sections ^[7]. So if you find one of them serving a ceiling light, you have found a defect.

For the remaining spaces, room type is a genuine but soft signal. Bedrooms, living rooms, and home offices commonly run on 15-amp circuits, because the loads are lamps, chargers, televisions, and small electronics. Garages, workshops, and unfinished basements more often run 20-amp circuits for power tools and heavier portable loads. Treat these as expectations to verify at the panel, never as conclusions.

Box fill: the physical half of compatibility

Getting the electrical rating right does not guarantee the outlet fits. Compatibility has a physical half — and it is worth separating the code question from the practical one, because they are not the same test.

The code question is box fill, and it is a calculation. NEC 314.16 requires a box to provide free space for all enclosed conductors, and states that the box volume calculated under 314.16(A) shall not be less than the fill calculated under 314.16(B) ^[1]. The fill count works from conductors and yokes rather than from how bulky a device looks. Each conductor originating outside the box and terminating or spliced inside counts once, as does each conductor passing straight through ^[1]. And for each yoke or strap containing devices, a double volume allowance is made based on the largest conductor connected to that yoke ^[1].

The gap between counting and clearance matters more than it first appears. Box fill does not penalize a device for being deep. A slim receptacle and a bulky one wired with the same conductors produce the same fill number. So passing the calculation does not tell you the device will seat.

The practical question is clearance, and it is physical. Receptacles containing electronics — charging circuitry, for example — have deeper bodies than a plain duplex outlet. In a shallow electrical box already crowded with conductors and splices, that body can run out of room even where the fill calculation is satisfied. Forcing it is not an option: compressing insulation to close a plate traps heat and damages the conductors. The remedies are a deeper or larger box, or a device with a shallower body.

Practical read: before buying a physically larger replacement, note the existing box depth and how many conductors are already in it. Older homes often have shallow boxes, and a retrofit or old work box set in plaster or drywall may have less usable volume than a new-construction box of the same face size. If the box is shallow, crowded, or a non-adjustable metal box in plaster, expect the physical fit to be the binding constraint rather than the amperage.

What to confirm before you buy a replacement

Once the branch is identified, choosing a replacement outlet is short work. In order of precedence:

1. Ampere rating and configuration. 15 A / NEMA 5-15R, or 20 A / NEMA 5-20R, matched to the branch as established above ^[2][10].
2. Whatever 406.4(D) requires for that location. GFCI, AFCI, tamper-resistant, or grounding-type as applicable ^[5][6][8][9]. This is a requirement list, not an options list.
3. A listing mark from a recognized testing laboratory. Every electrical outlet sold for this purpose is evaluated under UL 498 ^[11]; devices containing charging electronics carry additional evaluation on the electronics side. A listing mark and the standard it references are checkable facts about the device.
4. Physical fit. Body depth against the existing box, plus conductor count, per 314.16 ^[1].
5. Wiring method. Back-wire, side-wire, or both, chosen against the conductor layout you actually have in the box.

Everything below rating, code compliance, listing, and fit is preference. Convenience features do not change the branch-circuit requirement, and they never substitute for any item above them on this list.

That order of precedence is also a useful filter when comparing actual products. The first two items come out of your own box and cannot be shopped around. What a listing can settle for you is narrower: whether the device suits the conductor you already found, and whether it will physically go in.

ELEGRP's standard duplex receptacles split their terminals along exactly the line this article draws. On the 15-amp tamper resistant duplex receptacle, the quick push-in wiring is specified for #14 AWG solid copper while the side terminals take #12 AWG copper or copper-clad — so the conductor you identified at the box tells you which terminal to use, instead of leaving it to judgment. That model is self-grounding through a green grounding screw and a grounding clip, and it carries break-off plaster ears for squaring the yoke in an out-of-flush box, plus break-off tabs for splitting one duplex outlet across two circuits. The 20-amp version is a NEMA 5-20R duplex rated both tamper resistant and weather resistant, wired from the back or the side, with an automatic grounding clip for a properly grounded metal box. ELEGRP describes both as compact enough to leave working room in a standard junction box, which is the claim that matters once conductors and splices are already taking up volume. Both are UL Listed, both come in white and black, and neither ships with a wall plate, so budget for one. The wider range covers decorator styles, self-test GFCI, and USB-C charging outlets at store.elegrp.com.

None of that moves the order of decisions. Rating and configuration still come from the breaker and the conductor, the current requirements for the location still come from 406.4(D), and the body still has to fit the box. Matching the terminal to the conductor just removes one avoidable mistake from a job that already offers enough of them.

When to stop and call a licensed electrician

Some swaps are genuinely simple. Others announce themselves the moment the old device comes out.

Stop and bring in a licensed electrician if any of the following is true:

• Breaker size and conductor size disagree — for example, a 20-amp breaker on 14 AWG copper, which exceeds the 240.4(D) limit ^[4].
• Aluminum branch-circuit conductors are present.
• You find a single receptacle on what appears to be a dedicated circuit and the ratings do not satisfy 210.21(B)(1) ^[2][3].
• Signs of heat: discoloration on the device, scorched or brittle insulation, a warm faceplate, or melted slots.
• A breaker that trips repeatedly, which is a load or fault question rather than a device question.
• No equipment grounding means in the box, which brings 406.4(D)(1) into play ^[5].
• The box is overcrowded or damaged, or box fill under 314.16 is already at its limit ^[1].
• You cannot determine what else shares the branch, or the panel directory conflicts with what you found.

This is not about making a simple job sound intimidating. It is about not drawing a confident conclusion from incomplete evidence. A short professional check costs less than a misidentified circuit.

Frequently asked questions

Can a 15-amp receptacle be installed on a 20-amp circuit?

Yes, when the circuit supplies two or more receptacles. Table 210.21(B)(3) permits either a 15-amp or a 20-amp receptacle on a 20-amp branch circuit ^[2]. This pairing is very common in existing homes and is not a defect. The exception is a single receptacle on an individual branch circuit, which under 210.21(B)(1) must be rated no less than the circuit — so a lone receptacle on a dedicated 20-amp circuit has to be a 20-amp device ^[2][3].

Can a 20-amp receptacle be installed on a 15-amp circuit?

No. On a 15-amp branch circuit the permitted receptacle rating is 15 amperes ^[2]. The reason is the table itself, not appearance: a T-slot invites a 20-amp plug onto a circuit whose conductor is limited to 15 amperes under 240.4(D) ^[4]. If the breaker is 15 amps and the wiring is 14 AWG copper, the correct replacement is a 15-amp receptacle.

Does a T-shaped slot always mean the circuit is 20 amperes?

Nearly always, but confirm it anyway. Because a 20-amp receptacle is not permitted on a 15-amp circuit ^[2], finding one is strong evidence of a 20-amp branch. It is not proof that the installation is correct — someone may have installed it improperly. The breaker and conductor size are what confirm the branch.

Will a 15-amp receptacle overheat on a 20-amp circuit?

Not when the installation is correct, and the code permits the pairing deliberately rather than by oversight ^[2]. Two things make it work. The breaker still limits the circuit to 20 amperes, so no single receptacle can be asked for more than the branch allows. And receptacles are evaluated under UL 498 with the side and rear terminals tested concurrently ^[11], so a device wired feed-through is assessed with current passing through its terminals rather than only with current drawn from its face. What does cause heating at a receptacle is a loose or back-stabbed connection, which is a workmanship issue rather than a rating mismatch.

What wire gauge goes with a 15-amp circuit, and what goes with 20?

In typical residential copper wiring, 14 AWG pairs with 15 amperes and 12 AWG pairs with 20 amperes. This is a fixed code limit, not a convention: NEC 240.4(D) caps overcurrent protection at 15 amperes for 14 AWG copper and 20 amperes for 12 AWG copper, and these values do not round up to the next standard breaker size ^[4]. Aluminum is more restrictive, with 12 AWG aluminum capped at 15 amperes ^[4].

Do I have to add GFCI or AFCI protection when I replace an old outlet?

Often yes, and this surprises people. Under 406.4(D)(2), a replacement outlet must have GFCI protection wherever 210.8 requires it — kitchens, bathrooms, garages, laundry areas, outdoors, and near sinks among them ^[5][8]. Under 406.4(D)(4), AFCI protection is required on replacements where the branch circuit requires it under 210.12, which covers most dwelling living areas ^[5][9]. Both device types must be installed in a readily accessible location ^[5].

Are tamper resistant outlets required by code?

Yes, in the locations the Code specifies, and on replacements as well as new work. Section 406.12 sets out where tamper-resistant receptacles are required, and 406.4(D)(5) requires a listed tamper-resistant device whenever a replacement is made at one of those outlets ^[5][6]. Shopping guides frequently present a tamper resistant outlet as an optional upgrade; in a covered location it is a code requirement, not a preference.

What is a tamper resistant outlet, and how does it work?

It is a receptacle with an internal shutter mechanism that blocks the slots until a plug engages both of them simultaneously. Inserting a single object — the failure mode the requirement exists to address — does not open the shutters. Functionally it is an ordinary receptacle: a tamper resistant duplex receptacle carries the same 15-amp or 20-amp rating and the same NEMA configuration as a non-TR device ^[10], so it does not change any of the circuit matching in this article.

What is the difference between AFCI and GFCI?

They address different hazards, and neither substitutes for the other. A GFCI compares outgoing and returning current and opens the circuit when they stop balancing — shock protection for people, required by location under 210.8 ^[8]. An AFCI detects the electrical signature of arcing and opens the circuit before an arc can ignite surrounding material — fire protection for the wiring, required by circuit under 210.12 ^[1]. The Code treats them as separate obligations on a replacement, at 406.4(D)(2) and 406.4(D)(4) respectively ^[5]. Dual-function devices providing both protections exist.

Where is AFCI protection required?

Section 210.12 defines it, and the definition works by circuit rather than by room ^[1] — which is why the answer is framed around branch circuits serving dwelling living areas rather than a room list like the GFCI one in 210.8 ^[8]. Two practical notes follow. The AFCI requirements in 210.12 have expanded across recent code editions, so the list that applies to you is the one in the edition your jurisdiction enforces ^[1]. And on a replacement, 406.4(D)(4) carries the requirement forward: where the branch circuit requires AFCI protection elsewhere in the Code, the replacement receptacle outlet needs it too ^[5][9].

How many amps is a standard wall outlet?

In US dwellings, standard receptacles are 120-volt devices rated either 15 or 20 amperes, and the rating that matters is the branch circuit's rather than the device's alone. The device rating tells you what that part is rated for; the breaker and conductor tell you what the circuit is ^[2][4]. A 15-amp receptacle is the most common format, and it is permitted on both 15-amp and 20-amp branch circuits ^[2].

Does a USB or otherwise feature-rich receptacle change the amperage requirement?

No. Added functions do not change the branch-circuit rating or the permitted receptacle configuration. The device still has to match the breaker and conductor, still has to satisfy whatever 406.4(D) requires for that location, and still has to fit the box under 314.16 ^[1][2][5]. Features sit below compatibility in the order of decisions, never above it.

Which rooms are required to have 20-amp circuits?

Three cases are specified directly rather than left to judgment ^[7]. Kitchen and dining areas require two or more 20-ampere small-appliance branch circuits for the outlets listed in 210.52(B). Laundry requires at least one additional 20-ampere branch circuit. Bathrooms require at least one 120-volt, 20-ampere branch circuit that serves no other outlets. Those circuits may supply only the receptacle outlets specified in their own sections ^[7].

Why will the new receptacle not fit in the old box?

Because rating and fit are separate constraints. NEC 314.16 limits what a box of a given volume may contain, counting conductors, devices, clamps, and grounding conductors ^[1]. A device with a deeper body — one containing electronics, for instance — takes up more of that volume, so a correctly rated replacement can still fail to seat in a shallow or crowded box. The fix is a deeper or larger box, or a shallower device, not more force.

What if the breaker is 20 amps but the wire is 14 AWG copper?

Stop and treat it as a wiring defect. That combination exceeds the 240.4(D) limit of 15 amperes for 14 AWG copper ^[4]. The issue is not which receptacle to buy; it is that the conductor is protected above its permitted maximum. Have a licensed electrician determine whether the breaker should be reduced or the conductor replaced, and what else on the branch is affected.

Once I know the circuit is 20 amps, does that mean it can run what I want to plug in?

Those are two separate questions, and this article answers the first one. Identifying the rating tells you what the circuit is protected at and which receptacle belongs on it. Whether that circuit has enough capacity for a specific set of loads is a load calculation, which depends on what else shares the branch and how much of it runs at once. A correctly identified 20-amp circuit can still trip if the connected load exceeds it, so if you are adding a heavy appliance rather than replacing a device, treat capacity as its own question for a licensed electrician.

Do I need a permit to replace a receptacle?

That depends entirely on your jurisdiction, and it is worth checking before starting. NEC adoption, local amendments, permit thresholds, and whether a homeowner may perform electrical work are all decided locally rather than by the Code itself ^[1]. Your local building or electrical inspection office is the authority.

The bottom line

Choosing between a 15-amp outlet and a 20-amp outlet has a short answer and one commonly missed complication.

The short answer is two checks that must agree. The breaker gives the branch-circuit rating; the conductor gives the maximum that rating is permitted to be, with 14 AWG copper capped at 15 amperes and 12 AWG copper at 20 amperes under 240.4(D) ^[4]. Then read the face as confirmation, remembering the asymmetry: a 5-20R is strong evidence of a 20-amp branch, while a 5-15R is compatible with both and therefore tells you little ^[2].

The permitted pairings run one way. A 15-amp receptacle on a 20-amp circuit is allowed and normal; a 20-amp receptacle on a 15-amp circuit is not ^[2]. The single-receptacle-on-an-individual-circuit case reverses the usual guidance and is the exception most worth remembering ^[2][3].

The complication is that replacing a receptacle is not a like-for-like right. Section 406.4(D) requires the replacement to meet current requirements for that location, which can mean GFCI, AFCI, tamper-resistant, or grounding-type where the original device had none of them ^[5][6][8][9]. Getting the amperage right and the code requirements wrong still produces a non-compliant installation.

Add box fill under 314.16 as the physical constraint ^[1], and the full test for a replacement is four-part: correct rating, correct configuration, current code requirements for the location, and a body that actually fits the box. When any of the four is uncertain, the useful next step is a licensed electrician rather than a guess.

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References

1. NFPA 70, National Electrical Code — free read-only access, National Fire Protection Association Cited for the Code itself and for three sections read through transcription: 314.16, number of conductors in outlet, device, and junction boxes; 314.16(B)(4), device or equipment fill, which makes a double volume allowance per yoke based on the largest conductor connected to it; and 210.12, arc-fault circuit-interrupter protection. 314.16 transcription, UpCodes. box fill calculations. 314.16(B)(4) device or equipment fill.
2. NEC 210.21(B), receptacle ratings — Table 210.21(B)(3) and 210.21(B)(1), code text transcription, UpCodes The permitted receptacle rating for a branch circuit supplying two or more receptacles, and the stricter rule for a single receptacle on an individual branch circuit.
3. Receptacles in Dwellings — EC&M
4. NEC 240.4(D), small conductor overcurrent protection — code text transcription, UpCodes Fixed maximum overcurrent protection of 15 amperes for 14 AWG copper, 20 amperes for 12 AWG copper, 30 amperes for 10 AWG copper, and 15 amperes for 12 AWG aluminum, with no next-size-up allowance.
5. NEC 406.4(D), replacement of receptacles — code text transcription, UpCodes Replacements shall comply with 406.4(D)(1) through (D)(8) as applicable, and arc-fault and ground-fault circuit-interrupter type receptacles shall be installed in a readily accessible location.
6. NEC 406.4(D)(5) and 406.12, tamper-resistant receptacles — code discussion A listed tamper resistant receptacle is required where replacements are made at receptacle outlets required to be tamper-resistant elsewhere in the Code.
7. NEC 210.11(C)(1), (C)(2), (C)(3), required dwelling-unit branch circuits — code text transcription, UpCodes Two or more 20-ampere small-appliance branch circuits for the outlets in 210.52(B); at least one additional 20-ampere laundry branch circuit; at least one 120-volt, 20-ampere bathroom branch circuit serving no other outlets. small-appliance and laundry load provisions.
8. NEC 210.8, ground-fault circuit-interrupter protection for personnel — as adopted into S.C. Code Regs. § 8-1103, Cornell Legal Information Institute The location list that 406.4(D)(2) refers back to when a replacement requires GFCI protection. dwelling-unit application, manufacturer code reference.
9. Are there any other such receptacle replacement requirements? — IAEI Magazine, International Association of Electrical Inspectors
10. ANSI/NEMA WD 6-2021, Wiring Devices — Dimensional Specifications — standard record, ANSI Webstore Cited for configuration naming and for the existence of the dimensional standard that makes the 5-15R and 5-20R faces standardized rather than manufacturer styling. No dimensions are quoted here. publisher's standard page, NEMA. free preview excerpt.
11. UL 498, Standard for Safety for Attachment Plugs and Receptacles, 15th Edition — UL Standards & Engagement The receptacle-side evaluation basis for wiring devices, cited for the requirement that receptacles be tested with the side and rear terminals used concurrently, which is what makes a feed-through wired device's terminals part of the evaluated condition. concurrent-terminal testing described, IAEI Magazine.