For standard 120V/240V residential branch circuits using copper wire, the baseline rule is simple: a 15A breaker requires 14 AWG wire, a 20A breaker requires 12 AWG, and a 30A breaker requires 10 AWG. This circuit breaker sizes chart gives you the exact wire-to-breaker mapping based on the National Electrical Code (NEC). Bookmark this page, find your gauge, and pull the right breaker off the shelf.
How to Read This Circuit Breaker Sizes Chart
Before matching a breaker to a wire, you must understand which temperature column applies to your installation. This chart is sourced directly from NEC Article 310.16 (Ampacities of Insulated Conductors) and Article 240.4(D) (Small Conductors).
The NEC publishes ampacity based on the insulation's temperature rating, but your breaker terminations are typically rated for 75°C. More importantly, NEC 334.80 mandates that NM-B cable (commonly known as Romex) must be sized using the 60°C column, regardless of the fact that the physical wire insulation is rated for 90°C. If you are pulling individual THHN/THWN wires through conduit, you can use the 75°C column for ampacity, provided your breaker and device terminations are also rated for 75°C (which nearly all modern residential gear is).
The Master Circuit Breaker Sizes Chart (Copper)
Use the quick-jump links below to find your specific wire gauge. This table assumes copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway.
| AWG Size | 60°C Ampacity (NM-B / Romex) | 75°C Ampacity (THHN in Conduit) | Max Standard Breaker Size |
|---|---|---|---|
| 14 AWG | 15A | 20A | 15A (NEC 240.4(D) limit) |
| 12 AWG | 20A | 25A | 20A (NEC 240.4(D) limit) |
| 10 AWG | 30A | 35A | 30A (NEC 240.4(D) limit) |
| 8 AWG | 40A | 50A | 40A or 50A |
| 6 AWG | 55A | 65A | 60A |
| 4 AWG | 70A | 85A | 80A |
| 3 AWG | 85A | 100A | 100A |
| 2 AWG | 95A | 115A | 110A or 125A |
| 1 AWG | 110A | 130A | 125A |
| 1/0 AWG | 125A | 150A | 150A |
| 2/0 AWG | 145A | 175A | 175A |
| 3/0 AWG | 165A | 200A | 200A |
| 4/0 AWG | 195A | 230A | 225A or 250A |
Source: Copper Development Association & NEC 2023/2026 Article 310.16.
Derating and Edge Cases: When the Chart Changes
The chart above represents ideal conditions. In the real world, heat kills insulation, and you must adjust your wire size or breaker size when conditions change. This is called derating.
Bundling (More than 3 Current-Carrying Conductors)
Under NEC 310.15(C)(1), if you pull more than three current-carrying conductors through a single conduit, the wires heat each other up. You must multiply the 75°C or 90°C ampacity by a derating factor. Neutral wires carrying unbalanced current count as current-carrying; grounding wires do not.
- 4 to 6 conductors: Derate to 80%
- 7 to 9 conductors: Derate to 70%
- 10 to 20 conductors: Derate to 50%
30A × 0.80 = 24A.
Your wire is now legally limited to 24A. The next standard breaker size down is 20A. You must use a 20A breaker, not a 25A or 30A.
Ambient Temperature
If your conduit runs through an attic where temperatures regularly exceed 86°F (30°C), you must apply temperature correction factors from NEC Table 310.15(B)(1). A 12 AWG wire in a 110°F attic loses roughly 15% of its ampacity before bundling derating is even applied.
Decision Path: Pick Your Exact Breaker and Wire
Stop guessing. Use this decision-tree-table to terminate your planning phase with a concrete materials list.
| Installation Scenario | Load Requirement | Concrete Pick: Wire | Concrete Pick: Breaker |
|---|---|---|---|
| Standard 120V wall receptacles (bedrooms, living rooms) | 15A max | 14 AWG NM-B (12 AWG preferred for voltage drop) | 15A Single-Pole (or 20A if using 12 AWG) |
| Kitchen countertop outlets, bathroom GFCI, outdoor receptacles | 20A max | 12 AWG NM-B | 20A Single-Pole (AFCI/GFCI as required) |
| Electric dryer (standard 4-prong) | 30A max | 10 AWG NM-B (or 10 AWG THHN in conduit) | 30A Double-Pole |
| Electric range / oven | 40A to 50A | 6 AWG NM-B (for 50A) or 8 AWG (for 40A) | 50A Double-Pole (or 40A) |
| 100A Subpanel feeder (short run, < 50ft) | 100A max | 3 AWG THHN Copper (or 1/0 AWG Aluminum SER) | 100A Double-Pole |
| 200A Main Service / Subpanel feeder | 200A max | 2/0 AWG Copper or 4/0 AWG Aluminum | 200A Main Breaker |
What This Chart Cannot Tell You
Ampacity charts are the foundation of safe wiring, but they are not the entire codebook. Before you close up the panel, verify these three critical factors that the chart above does not cover:
- Voltage Drop on Long Runs: The NEC recommends a maximum 3% voltage drop for branch circuits. If you are running a 20A circuit to a detached garage 120 feet away, 12 AWG wire will suffer excessive voltage drop under load. You must upsize to 10 AWG or 8 AWG to maintain voltage, but you still terminate it on a 20A breaker. Upsizing wire for distance does not allow you to increase the breaker size.
- Continuous Load Rules (The 80% Rule): Under NEC 210.20(A), if a load is expected to run for 3 hours or more (like a space heater, EV charger, or hardwired lighting), the breaker must be rated at 125% of the continuous load. A 20A breaker can only handle 16A of continuous load. If your EV charger draws 16A continuously, you need a 20A breaker. If it draws 32A continuously, you need a 40A breaker and 8 AWG wire.
- Interrupting Capacity (AIC Rating): The chart tells you the thermal limit of the wire, but not the short-circuit interrupting capacity of the breaker. Standard residential breakers are rated for 10,000 Amps Interrupting Capacity (10kA IC). If your home is located very close to the utility transformer, the available fault current might exceed 10kA, requiring you to buy 22kA IC breakers (often marked with a 'H' or specific label on the breaker face).
Always treat NEC-style guidance as the baseline minimum. Your local Authority Having Jurisdiction (AHJ) or municipal inspector has the final authority on your specific installation. When in doubt, pull a permit and have the work inspected.
