20 amp wire size
A 20 amp circuit needs 12 AWG copper wire with 75 °C terminations. Aluminum wire is not used for circuits this small.
20 amp wire size by termination rating
| Termination rating | Copper | Aluminum |
|---|---|---|
| 60 °C, NM-B | 12 AWG | copper only |
| 75 °C, THHN | 12 AWG | copper only |
| Ground wire | 12 AWG | — |
20 amp wire size by distance at 120 V
Sizes that keep the voltage drop within 3% on a 120 V circuit loaded to the full 20 A, 75 °C terminations. The copper ground wire grows with the hot wires on long runs.
| One-way distance | Copper | Drop | Copper ground |
|---|---|---|---|
| 25 ft | 12 AWG | 1.6% | 12 AWG |
| 50 ft | 10 AWG | 2.1% | 10 AWG |
| 100 ft | 8 AWG | 2.6% | 8 AWG |
| 150 ft | 6 AWG | 2.5% | 6 AWG |
| 200 ft | 4 AWG | 2.1% | 4 AWG |
| 300 ft | 3 AWG | 2.5% | 3 AWG |
Check your own 20 amp run
What are you sizing for?
A
ft
From the panel to the load, not there and back
Voltage
Conductor
Termination rating
Result
10 AWG copper
The run is long: ampacity alone allows 12 AWG, but a larger wire keeps the drop within 3%.
- Breaker
- 20 A
- Voltage drop
- 2.5 V (2.1%)
- Volts at the load
- 117.5 V
- Ground wire
- 10 AWG copper
How it is calculated
- Breaker: 20 A rounded up to a standard size = 20 A.
- Smallest copper conductor rated for 20 A at 75 °C: 12 AWG.
- Drop = 2 × K × 20 A × 50 ft ÷ 10,380 cmil = 2.49 V, target 3% of 120 V.
What a 20 amp circuit is used for
- Kitchen and bathroom outlets
- Garage outlets
- Microwave or dishwasher on a dedicated circuit