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Wire Gauge Calculator

Calculate proper wire size (AWG)

Result

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NEC Ampacity (75°C)

AWG	Copper	Aluminum
14	20A	—
12	25A	20A
10	35A	30A
8	50A	40A
6	65A	50A
4	85A	65A
2	115A	90A

Common Applications

14 AWG: 15A circuits, lighting
12 AWG: 20A circuits, outlets
10 AWG: 30A circuits, dryers
8 AWG: 40A circuits, ranges
6 AWG: 50-60A, sub-panels

Understanding Wire Gauge Selection

Selecting the correct wire gauge is critical for electrical safety and performance. Wire that's too small will overheat, potentially causing fires. Wire that's unnecessarily large wastes money and is harder to work with.

Two Key Factors

1. Ampacity: The wire must safely carry the required current without overheating. This is the minimum wire size based on NEC tables.

2. Voltage Drop: For long runs, you may need larger wire to limit voltage drop to acceptable levels (typically 3% or less).

Understanding AWG

American Wire Gauge (AWG) uses a counter-intuitive numbering system: smaller numbers = larger wire. Each decrease of 3 AWG doubles the cross-sectional area. Each decrease of 6 AWG doubles the ampacity. AWG 4/0 (0000) is larger than AWG 1.

NEC Requirements

The National Electrical Code specifies minimum wire sizes for different ampacities. For branch circuits: 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A. Always use the larger of ampacity-based or voltage-drop-based sizing.

Frequently Asked Questions

For 20 amps, use 12 AWG copper wire minimum per NEC. For aluminum, use 10 AWG. For runs over 50 feet, calculate voltage drop - you may need 10 AWG copper to keep voltage drop under 3%.

AWG is the US standard for wire sizing. Lower numbers = thicker wire = more capacity. Each 3 AWG decrease doubles the wire area. Each 6 AWG decrease roughly doubles the ampacity. Sizes go: 14, 12, 10, 8, 6, 4, 2, 1, 1/0, 2/0, 3/0, 4/0.

Use: CM = (2 × K × I × L) / VD, where CM is circular mils, K is 12.9 for copper or 21.2 for aluminum, I is current in amps, L is one-way distance in feet, and VD is maximum voltage drop in volts. Match result to standard sizes.

Copper has 60% better conductivity, is easier to terminate, and doesn't require special connectors. Aluminum is cheaper and lighter but needs 2 sizes larger for same ampacity. Aluminum requires anti-oxidant compound and AL-rated devices. Use copper for branch circuits, aluminum for large feeders.

For 50 amps: use 6 AWG copper or 4 AWG aluminum minimum. For ranges/ovens, NEC allows 8 AWG for existing installations. For long runs (over 100 feet), consider 4 AWG copper to limit voltage drop.

Longer wire = more resistance = more voltage drop. While a wire might safely carry the current (ampacity), the voltage at the load may be too low if the wire is undersized for the distance. Motors are especially sensitive to low voltage.

For continuous loads (running 3+ hours), NEC requires wire rated for 125% of load (or load limited to 80% of wire ampacity). A 20A circuit with continuous load should carry only 16A (20 × 0.8). Size breakers and wire accordingly.

Yes, using larger wire is always acceptable and reduces voltage drop. The only downsides are cost and difficulty fitting larger wire in boxes/conduit. Never use smaller wire than required - that's a code violation and fire hazard.