NEC 240.6(A)
Standard Breaker Sizes (NEC 240.6(A))
Enter an amperage and get the standard device to buy, the conductor it needs, and whether the NEC 240.4(B) round-up is available on your circuit.
free round-up
Standard breaker sizes are fixed, but the size you may actually use is not. NEC 240.6(A) prints the ladder; what a given conductor may be protected at depends on its ampacity, on your termination column, and on three conditions in 240.4(B) that this page evaluates one at a time. A 55 A calculated load takes a 60 A device on #6 copper. A 22 A load does not take a 25 A device on #12 copper, and the reason is the part most references leave out.
240.4(D) outranks the round-up, and this page used to say otherwise. It previously answered “can I round up to the next standard breaker size?” with “Usually yes” and never mentioned 240.4(D). That was wrong for the commonest case there is. 240.4(D) reads “unless specifically permitted in 240.4(E) or (G)”, and 240.4(B) is not on that list, so 14 AWG copper stays at 15 A, 12 AWG copper at 20 A and 10 AWG copper at 30 A no matter what the round-up appears to allow. Inside Article 440 the caps do lift, through 240.4(G).
The ampere figure you have already worked out. If the load is continuous this should already be the 125 percent figure from 210.20(A); this screen does not apply it for you.
On a circuit rated 100 A or less, 110.14(C)(1)(a) puts you in the 60°C column unless the equipment is listed and marked for 75°C. Most modern breakers and panelboards are marked 60/75°C, but that is a marking on the gear, not something this screen can see.
Table 240.4(G) sends air-conditioning and refrigeration circuit conductors to Article 440, Parts III, IV and VI for their overcurrent protection, and that is what lifts the small-conductor caps on those circuits. It is the only one of Table 240.4(G)’s ten applications this tool models. The others, motor and motor-control circuits under Article 430 most commonly, lift the caps by the same mechanism and are not computed here, so on one of those this screen will be more restrictive than the code is.
NEC 240.4(B), condition by condition on this circuit
Conditions (1) and (3) are satisfied on this circuit. Condition (2) is not a fact about the circuit: it is checked against each conductor, and the answer above says whether it changed the size.
Where this number comes fromIntry Verified
- Calculated from
- NEC Table 240.6(A) standard ampere ratings, with 240.4(B) next-higher-standard-device, the 240.4(D) small-conductor limits and the 240.4(G) Article 440 exception, conductor ampacity from NEC Table 310.16 at the 110.14(C) column, grounding conductor from Table 250.122. Computed from NEC Table 240.6(A), with the 240.4(B) next-higher-device permission evaluated condition by condition, the 240.4(D) small-conductor caps applied over it, and the conductor read from Table 310.16 at your 110.14(C) column. See the full receipt ↓
- Run with
- Amperage55 A
- Conductor materialcopper
- Terminations75°C
- Multi-receptacle cord-and-plug circuitno
- Article 440 circuitno
- Standard device60 A
- Checked
- Every figure an Intry calculator computes comes from a locked source module, not hand-typed. 21026 automated checks re-derive and source-check the numbers against the cited NEC section before each deploy. This is our own deterministic gate, not a third-party audit.
- Final say
- Your AHJ and local amendments have final say. Confirm before rough-in.
Intry Verified · NEC 2023 · Build AE2FC52 · 2026-08-21
| Conductor | Ampacity at 75°C | 240.4(D) cap | Largest device here |
|---|---|---|---|
| #14 | 20 A | 15 A | 15 A |
| #12 | 25 A | 20 A | 20 A |
| #10 | 35 A | 30 A | 30 A |
| #8 | 50 A | – | 50 A |
| #6 | 65 A | – | 70 A |
| #4 | 85 A | – | 90 A |
| #3 | 100 A | – | 100 A |
| #2 | 115 A | – | 125 A |
| #1 | 130 A | – | 150 A |
| #1/0 | 150 A | – | 150 A |
| #2/0 | 175 A | – | 175 A |
| #3/0 | 200 A | – | 200 A |
The last column is the one a printed roster of standard ratings cannot carry: it depends on your termination column, on whether the round-up is available on your circuit, and on whether Article 440 applies, none of which the table in the book knows. Rows in red are where the 240.4(D) small-conductor cap, not the ampacity, is what limits the device.
The Next-Standard-Size Rule, As It Is Printed
Conductor ampacities from NEC Table 310.16 rarely land exactly on a standard device rating, so 240.4(B) gives a rounding rule: the next higher standard rating above the conductor ampacity is permitted, provided all three of the following are true. One, the conductors are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads. Two, the conductor’s ampacity does not already correspond with a standard fuse or breaker rating, because if it does, the conductor is simply protected at that rating and there is nothing to round. Three, the next higher rating selected does not exceed 800 amperes. Above 800 A, 240.4(C) reverses the rule entirely: the conductor ampacity must be equal to or greater than the device rating.
⚠ Two of those three used to be stated loosely on this page, and both are now taken from the printed text. Condition one was written as “not a receptacle multioutlet circuit”, which is not what the code says and is both broader and vaguer than “more than one receptacle for cord-and-plug-connected portable loads”. Condition two was written as “the next size up is genuinely the next standard value”, which is not a condition at all; the real one is about whether the conductor’s own ampacity already lands on a standard rating.
What This Page No Longer Publishes
This page used to reproduce the whole of Table 240.6(A) as a standalone chart and again as a comma-separated list. It now computes against that table instead of republishing it. The scope is worth stating plainly either way: Table 240.6(A)’s first rating is 10 A, and the sentence following the table adds 1, 3, 6 and 601 A as standard ratings for fuses only, which a circuit breaker may not use. The tool above is scoped to the 15 A-and-up breaker ladder, which is where branch and feeder sizing actually lands, and it reads the full 240.6(A) roster including 10 A when it reports the next standard size down. Sizing a device below 15 A, or specifying a fuse at 1, 3, 6 or 601 A, is outside what this page covers.
Frequently Asked Questions
What are the standard breaker sizes?
NEC 240.6(A) sets the standard ratings, and the useful thing is the shape of the ladder rather than the whole list. From 15 A it climbs in 5 A steps to 50 A, then in 10 A steps to 100 A, then in widening jumps through the 100s and 200s, and above 250 A the gaps are 50 A or more. That is why there is no standard 55 A, 65 A or 130 A device. Below the breaker range the table starts at 10 A, and the sentence after it adds 1, 3, 6 and 601 A as ratings for fuses only, which a circuit breaker may not use. Enter your amperage in the calculator on this page and it returns the standard device at or above it, the next one below it, and the conductor each requires.
Is there a 55 amp breaker?
No, 55A is not a standard size in NEC 240.6(A). The standard ratings jump from 50A to 60A, so a 55A calculated load is normally protected at 60A. Nonstandard ratings do exist as listed devices but are not part of the standard 240.6(A) set.
What is the next standard breaker size above 70 amps?
The next standard size above 70A is 80A, then 90A, then 100A, per NEC 240.6(A). Below 70 the standard ratings are 30, 35, 40, 45, 50, 60, and 70 (5A steps up to 50, then 10A steps to 60 and 70).
Can I round up to the next standard breaker size?
Sometimes, and not on the small conductors people most often ask about. NEC 240.4(B) permits the next higher standard rating above the conductor ampacity when all three of its conditions are met: the conductors are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads, the conductor ampacity does not already correspond with a standard rating, and the next higher rating does not exceed 800 A. But 240.4(D) caps 14 AWG copper at 15 A, 12 AWG copper at 20 A and 10 AWG copper at 30 A, and it says those caps are lifted only by 240.4(E) or 240.4(G). It does not name 240.4(B), so the round-up cannot raise a device above them: you go to the larger conductor, not the larger breaker. Article 440 air-conditioning and refrigeration circuits are the common exception, through 240.4(G). Above 800 A, 240.4(C) requires the conductor ampacity to equal or exceed the device rating.
Can I put a 25 amp breaker on 12 gauge wire?
No, not on an ordinary branch circuit. 12 AWG copper is capped at 20 A by NEC 240.4(D)(6) even though its 75C ampacity is 25 A, and the 240.4(B) next-size-up permission does not lift that cap because 240.4(D) names only 240.4(E) and (G) as the provisions that can. A 22 A load takes 10 AWG copper on a 25 A device. The exception is an Article 440 air-conditioning or refrigeration circuit, where Table 240.4(G) sends the conductors to Article 440 for overcurrent protection and the small-conductor caps do not apply.
What are the standard breaker sizes over 100 amps?
Above 100 A the steps widen progressively: two more closely spaced ratings just above 100, then 25 A steps up into the 200s, 50 A steps through the 300s and 400s, and 100 A steps to 800. Past 800 A the jumps get much larger, and 240.4(C) changes the rule as well: above 800 A the conductor ampacity must be equal to or greater than the device rating, so the next-size-up round-up of 240.4(B) is not available at all. Enter your amperage above and the calculator returns the exact standard device and the conductor it needs.
Related Calculators & Charts
Wire Ampacity Chart (310.16)
Match a conductor ampacity to the right standard breaker against what a conductor actually carries in your conditions.
Wire Size Calculator
Size the conductor for a load and get the breaker that protects it, rounding handled.
Ground Wire Size Chart (250.122)
The equipment grounding conductor is sized from that breaker rating, look it up here.
Have the sizes. Now match one to your load.
The right breaker depends on the conductor ampacity and the load type. The wire size calculator sizes the conductor and picks the standard breaker that protects it.
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