Wire Size to Breaker Size Chart: AWG, Ampacity & NEC Sizing Guide

For standard residential copper branch circuits, match 14 AWG to a 15A breaker, 12 AWG to a 20A breaker, 10 AWG to a 30A breaker, 8 AWG to a 40A or 50A breaker, and 6 AWG to a 55A or 60A breaker. These pairings are dictated by the National Electrical Code (NEC) Table 310.16 and the small conductor rules in NEC 240.4(D). Sizing is never about simply matching the wire's maximum thermal limit to the breaker; it is about protecting the weakest point in the circuit, which is usually the termination lug at the breaker or receptacle.

How to Read This Wire Size to Breaker Size Chart

Before looking at the numbers, you must understand the temperature columns. Wire insulation like THHN is rated for 90°C, but you rarely get to use that full capacity. The column you must use is determined by NEC 110.14(C), which governs termination temperature limits.

The chart below assumes copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway. If your installation deviates from these baselines, you must apply derating factors (covered below).

The Master Wire Size to Breaker Size Chart (NEC Table 310.16)

This table provides the allowable ampacities for insulated copper conductors. The "Max Standard Breaker" column reflects the next-size-up rule (NEC 240.4(B)) and the hard limits for small conductors (NEC 240.4(D)).

Source: Data derived from NFPA 70 (NEC) Table 310.16. Always verify against the specific edition adopted by your local Authority Having Jurisdiction (AHJ).

Decision Path: Picking Your Exact Wire and Breaker

Use this if-then decision tree to lock in your materials list for standard 120V/240V residential branch circuits. This path assumes copper wire and standard termination ratings.

• If your calculated continuous load is 12A or less (e.g., standard lighting, 15A receptacles): Pick 14 AWG copper wire and a 15A single-pole breaker.
• If your calculated continuous load is 16A (e.g., kitchen counter small-appliance circuits, bathroom GFCI): Pick 12 AWG copper wire and a 20A single-pole breaker.
• If your load is a standard electric water heater or window AC unit drawing up to 24A: Pick 10 AWG copper wire and a 30A double-pole breaker.
• If your load is an electric range or cooktop drawing up to 40A: Pick 8 AWG copper wire and a 40A double-pole breaker. (If the manufacturer specifies 50A and terminals are 75°C rated, use 8 AWG with a 50A breaker).
• If your load is an EV charger or subpanel feeder drawing up to 48A continuous (60A non-continuous): Pick 6 AWG copper wire and a 60A double-pole breaker.
• If your load is a 100A subpanel feeder: Pick 3 AWG copper wire (or 1 AWG aluminum) and a 100A double-pole breaker.

Derating Factors: When Base Ampacity Drops

The ampacity numbers in the chart above are "base values." They assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single conduit. When conditions change, the wire's ability to shed heat drops, and you must derate the ampacity using the 90°C column as your starting point, per NEC 310.15(C)(1).

How derating modifies the base value: If you pull four current-carrying conductors (e.g., two 120V circuits sharing a neutral, or a 240V circuit with a neutral) through a single conduit, you must apply an 80% derating factor.

Worked Example: You are running two 20A circuits in one conduit using 12 AWG THHN. 1. Start at the 90°C column for 12 AWG: 30A. 2. Apply the 80% derating factor for 4-6 conductors: 30A × 0.80 = 24A. 3. The derated ampacity of the wire in the conduit is 24A, which safely protects the wire from overheating inside the pipe. 4. However, because of NEC 110.14(C), your breaker and receptacle terminations are still limited to the 60°C or 75°C column (20A or 25A). Therefore, you still terminate on a 20A breaker. The 90°C column is almost exclusively used as a mathematical starting point for derating calculations, not for selecting breaker sizes.

For a comprehensive look at how ambient temperatures above 86°F further reduce these values, consult the Copper Development Association's wire sizing guidelines, which provide detailed ambient temperature correction factors.

What This Chart Cannot Tell You

A wire size to breaker size chart is a baseline safety tool, not a complete engineering blueprint. It will not account for the following critical variables:

1. Voltage Drop Over Distance: NEC 310.16 does not enforce voltage drop limits (it only enforces thermal limits), but NEC 210.19(A) Informational Notes recommend keeping branch circuit voltage drop under 3%. If you are running a 20A circuit to a detached garage 150 feet away, 12 AWG wire will suffer a voltage drop exceeding 3%. You must upsize to 10 AWG or 8 AWG to maintain voltage, even though your breaker remains 20A.
2. Continuous Load Multipliers: If a load will run for 3 hours or more continuously (like a hardwired space heater, commercial lighting, or an EV charger), NEC 210.20(A) requires the breaker to be sized at 125% of the continuous load. A 16A continuous EV charger requires a 20A breaker (16 × 1.25 = 20), and the wire must also be sized to carry 125% of the load.
3. Specific Appliance Mandates: Manufacturer installation instructions override general charts. A 3-ton HVAC condenser might have a Maximum Overcurrent Protection (MOP) of 40A but a Minimum Circuit Ampacity (MCA) of 24A. In this case, you must use 10 AWG wire (rated for 30A/35A) protected by a 40A breaker, because the manufacturer's listed instructions dictate the exact pairing under NEC 110.3(B).

Always default to the manufacturer's nameplate data for hardwired appliances. For general branch circuits, stick strictly to the 60°C/75°C termination limits, apply your derating math for conduit fill, and upsize for long runs. When in doubt, moving up one AWG size costs slightly more in copper but guarantees compliance and eliminates thermal bottlenecks at the lug.