Minimum wire size by breaker rating
The smallest wire size whose NEC Table 310.16 ampacity is at least the breaker rating, with the small-conductor limits of 240.4(D). The 60°C column applies to NM-B (Romex) cable and to equipment with 60°C terminals. The 75°C column applies to THHN or THWN wire in conduit on 75°C-rated terminals.
| Breaker | Copper, 60°C / NM-B | Copper, 75°C | Aluminum, 75°C | Aluminum, 60°C |
|---|---|---|---|---|
| 15 A | 14 AWG | 14 AWG | 12 AWG | 12 AWG |
| 20 A | 12 AWG | 12 AWG | 10 AWG | 10 AWG |
| 25 A | 10 AWG | 10 AWG | 10 AWG | 10 AWG |
| 30 A | 10 AWG | 10 AWG | 8 AWG | 8 AWG |
| 35 A | 8 AWG | 8 AWG | 8 AWG | 6 AWG |
| 40 A | 8 AWG | 8 AWG | 8 AWG | 6 AWG |
| 45 A | 6 AWG | 8 AWG | 6 AWG | 4 AWG |
| 50 A | 6 AWG | 8 AWG | 6 AWG | 4 AWG |
| 60 A | 4 AWG | 6 AWG | 4 AWG | 3 AWG |
| 70 A | 4 AWG | 4 AWG | 3 AWG | 2 AWG |
| 80 A | 3 AWG | 4 AWG | 2 AWG | 1 AWG |
| 90 A | 2 AWG | 3 AWG | 2 AWG | 1/0 AWG |
| 100 A | 1 AWG | 3 AWG | 1 AWG | 1/0 AWG |
| 110 A | 1 AWG | 2 AWG | 1/0 AWG | 2/0 AWG |
| 125 A | 1/0 AWG | 1 AWG | 2/0 AWG | 3/0 AWG |
| 150 A | 3/0 AWG | 1/0 AWG | 3/0 AWG | 4/0 AWG |
| 175 A | 4/0 AWG | 2/0 AWG | 4/0 AWG | n/a |
| 200 A | n/a | 3/0 AWG | n/a | n/a |
Sizes are minimums for ampacity. Add distance, a hot location, bundled circuits or continuous loads, and the wire may need to go up.
Guides for the most common breakers
- What size wire for 20 amps: receptacles and general circuits
- What size wire for 30 amps: dryers and water heaters
- What size wire for 40 amps: ovens and EV chargers
- What size wire for 50 amps: ranges, RVs and hot tubs
- What size wire for 60 amps: sub panels and large equipment
- What size wire for 100 amps: sub panels and small services
- What size wire for a 200 amp service: the main panel
Continuous loads
Loads that run for three hours or more, such as EV chargers and some heaters, must be sized at 125% of the load. A 32 A charger needs a 40 A circuit, and a 40 A charger needs a 50 A circuit. Pick the wire for the breaker, not the charger.
Ground wire
The equipment ground is sized from the breaker as well, using NEC Table 250.122: 14 AWG copper for 15 A, 12 AWG for 20 A, 10 AWG for 30 to 60 A and 8 AWG for 70 to 100 A. See the ground wire size calculator.
Frequently asked questions
What size wire for a 100 amp breaker?
3 AWG copper or 1 AWG aluminum at 75°C. A 100 amp dwelling service may use 4 AWG copper under NEC 310.12.
What size wire for a 30 amp breaker?
10 AWG copper, or 8 AWG aluminum.
Can I put a 20 amp breaker on 14 gauge wire?
No. 14 AWG copper is limited to a 15 amp breaker. Use 12 AWG for 20 amps.
What size wire for a 60 amp breaker?
6 AWG copper at 75°C, or 4 AWG for NM-B cable or 60°C terminals.