AWG Sizing Chart for Copper Wire: Ampacity and NEC Breaker Rules

For standard 120V and 240V residential branch circuits, the baseline AWG sizing rule is simple: 14 AWG handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. However, once you move beyond basic receptacle circuits into feeder sizing, subpanels, or conduit runs with multiple wires, relying on memory leads to failed inspections and fire hazards. Proper wire sizing requires cross-referencing the National Electrical Code (NEC) ampacity tables with termination temperature ratings and conduit fill derating factors.

How to Read the NEC AWG Sizing Table

The core reference for wire sizing in the United States is NEC Table 310.16, published by the National Fire Protection Association (NFPA). This table is divided into three distinct temperature columns for copper conductors: 60°C, 75°C, and 90°C. Knowing which column applies to your specific installation is the most common point of failure for DIYers and junior electricians.

Which column applies to your installation? According to NEC 110.14(C), the ampacity of a circuit is limited by the lowest temperature rating of any connected device, termination lug, or conductor in the run. Most standard residential circuit breakers under 100 amps are rated for 60°C or 75°C terminations. Non-metallic sheathed cable (NM-B, commonly known as Romex) is strictly limited to the 60°C column, regardless of the fact that its internal THHN wires are technically rated for 90°C. For circuits rated 100 amps or less, you must use the 60°C column unless the breaker and lugs are explicitly stamped "75°C". For circuits over 100 amps, the 75°C column is the standard baseline.

Complete AWG Sizing and Ampacity Reference Chart

Before scrolling to the full matrix, use these bookmark-friendly quick-jump rows to verify the most heavily queried residential and light-commercial sizes:

• 15A Branch (14 AWG): Standard lighting and general-use receptacles.
• 20A Branch (12 AWG): Kitchen, bathroom, and garage small appliance circuits.
• 30A Branch (10 AWG): Electric dryers, water heaters, and heavy window AC units.
• 60A Feeder (6 AWG): Common subpanel, hot tub, or EV charger supply.
• 100A Feeder (2 AWG): Standard residential subpanel or workshop supply.
• 200A Service (4/0 AWG): Main residential service entrance conductors.

Source: 2023 NEC Table 310.16 (Copper Conductors, 30°C Ambient Temperature). *Breaker sizing marked with an asterisk assumes 75°C terminations are verified on both the breaker and the load lugs. Otherwise, default to the 60°C column limit.

How derating rows modify the base value: The ampacities listed above assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway. If you pull four to six current-carrying conductors through one conduit, NEC 310.15(C)(1) requires you to apply an 80% adjustment factor. You apply this multiplier to the 90°C column ampacity, not the 60°C column. For example, if you have four 10 AWG THHN wires in a conduit, you take the 90°C rating (40A) and multiply by 0.80, yielding a derated ampacity of 32A. Because 32A still exceeds the 60°C termination limit of 30A, you are legally permitted to protect that circuit with a 30A breaker. If the derated value falls below your required load, you must upsize the wire.

What the AWG Sizing Table Cannot Tell You

While NEC Table 310.16 prevents wires from melting under continuous load, it completely ignores voltage drop. The NEC recommends (via Informational Note to 310.15(B)) that branch circuits be sized to limit voltage drop to 3%, and the total feeder-plus-branch drop to 5%. If you run a 12 AWG wire 100 feet to a 16-amp window air conditioner, the wire won't overheat, but the voltage at the receptacle will drop by roughly 6.4 volts (5.3%). The compressor will struggle to start, draw higher locked-rotor amperage, and eventually burn out. For long runs, always cross-reference your AWG sizing with a dedicated voltage drop calculator and upsize the wire accordingly.

Furthermore, the table cannot tell you if the wire will physically fit into your equipment. A 1/0 AWG copper wire is rated for 150A at 75°C, but many 150A main breaker lugs are physically designed to accept a maximum of 1/0 or 2/0. Conversely, trying to cram a stiff 4/0 AWG wire into a tight panel gutter can damage the insulation or result in a poor mechanical connection, leading to arcing and thermal failure at the lug. Always check the manufacturer's lug torque specs and physical wire range markings before purchasing feeder wire.