Amp wire chart — AWG and mm² for 15 to 800 A circuits

Use the calculator

The chart below is the NEC 310.16 standard lookup. The calculator applies all derating (continuous load, ambient, conductor count, parallel sets) and runs the voltage-drop check, so you get the smallest size that passes both tests for your actual installation.

NEC 310.16 amp-to-wire chart

Standard ampacity at 30°C ambient with no more than three current-carrying conductors in a raceway, no continuous-load adjustment. For continuous loads (≥3 hours at full current), divide the table value by 1.25 to get the breaker rating, or pick the next size up so the conductor's ampacity ≥ 1.25 × load.

The ampacities for conductors rated 0 through 2000 V shall be as specified in the Allowable Ampacity Table 310.16 through Table 310.20… Where the ambient temperature is other than 30°C (86°F), the ampacities shall be corrected by the factors in Table 310.15(B)(1)(1) for ambient temperature.

How to read the chart, step by step

1. Get the load current. Read the nameplate full-load amps (FLA) of the equipment, or compute from the load: I = P / V (DC), I = P / (V·cos φ) (1-phase), I = P / (√3·V·cos φ) (3-phase). For motors, use the NEC 430 table FLA, not the nameplate, when sizing branch wire.
2. Apply the continuous-load factor if applicable. NEC 210.19(A) — if the load runs ≥3 hours at full current (HVAC, EV chargers, lighting, water heaters), multiply by 1.25. The wire must carry this adjusted current after derating. EV chargers are explicitly continuous: a 32 A charger needs a 40 A breaker.
3. Pick the insulation column that matches your equipment terminations. NEC 110.14(C) caps the effective rating to 60°C for most circuits ≤100 A unless the device is listed for higher; for >100 A circuits and modern equipment, the 75°C column is the practical limit. The 90°C column is used as a starting point for derating math, not for direct sizing.
4. Look up the AWG that meets the derated ampacity. Find the smallest size in NEC Table 310.16 (or the chart on this page) whose tabulated ampacity, after multiplying by ambient and conductor-count correction factors, ≥ adjusted load. Verify against NEC 240.4(D) — 14/12/10 AWG copper is capped at 15/20/30 A regardless of insulation.
5. Cross-check voltage drop on the chosen size. For runs longer than ~30 m at 240 V or ~15 m at 120 V, check that V_drop = 2·L·I·ρ/A ≤ 3% branch (5% combined). If voltage drop fails, step up one or more sizes. The calculator embedded above runs this check automatically.
6. Pick the breaker and the equipment grounding conductor. Round the load up to the next standard breaker per NEC 240.6(A): 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200 A. Look up the minimum EGC from NEC Table 250.122 based on that breaker rating, not the wire size.

Standard household and small-commercial circuits

Most US residential branch circuits are one of the standard amperages below. The wire size assumes 75°C copper, ≤30 m one-way run, ≤3 conductors in conduit. Always size up if voltage drop on your run exceeds 3%.

Two important caveats: NEC 240.4(D) caps the breaker on 14, 12, and 10 AWG copper at 15, 20, and 30 A even if the insulation rating allows higher. And NEC 310.12 has a special reduced-ampacity rule for 100–400 A dwelling-unit service entrances and feeders supplying the entire dwelling — 4 AWG Cu / 2 AWG Al for 100 A, 2/0 Cu / 4/0 Al for 200 A.

Wire size for major appliances

Each appliance below has its own typical breaker and wire size. Always read the nameplate — actual current draw varies by model, especially for heat-pump and inverter-driven equipment.

For continuous loads — anything that runs ≥3 hours at full current — NEC 210.19(A) requires the conductor's ampacity to be ≥1.25 × the load. EV chargers are continuous; that is why a 32 A charger needs a 40 A breaker (32 × 1.25), not a 30 A one. The calculator handles this factor automatically when you pick the EV-charging or "continuous" preset.

How length and voltage drop change the answer

The chart sets the absolute floor — the smallest wire that can safely carry the current as heat. On almost every real installation, voltage drop pushes you to a larger wire, especially at 120 V or DC, and on long runs of small wire.