What Size Wire for 15, 20, 30, 40 and 50 Amps? AWG Chart

For the current alone, copper needs 14 AWG for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, 8 AWG for 40 amps (and for 50 amps at 75°C), and 6 AWG for 50 to 65 amps (at 75°C, or for 50 amps in ordinary cable). Long runs need a bigger wire to limit voltage drop. The wire size calculator gives the size for your current, voltage and distance.

Smallest wire for the current

From the NEC ampacity table (three or fewer conductors at 86°F) with the small-wire breaker limits. The 60°C column applies to older or small equipment, and 75°C to most modern breakers and panels:

Wire size for longer runs

To keep the voltage drop under 3%. 20 and 30 amps at 120 V, and 50 amps at 240 V, copper at 75°C:

Use the voltage drop calculator to check a particular wire.

The rules behind the chart

• Ampacity: each wire size can carry a limited current without overheating. The table depends on the temperature rating of the insulation and the terminals.
• Small wire limits: 14 AWG copper is limited to a 15 amp breaker, 12 AWG to 20 amps and 10 AWG to 30 amps, even though the wire could carry more.
• Continuous loads: size the wire and the breaker for 125% of a load that runs three hours or more.
• Voltage drop: keep it to 3% or less on a branch circuit, which means a bigger wire for a long run or a low voltage.
• Derating: more than three wires in a conduit, or a hot location, reduces the ampacity.
• Aluminum: needs a larger size than copper for the same current, and connectors rated for it.

AWG: how the numbers work

American Wire Gauge numbers go the wrong way: a smaller number is a thicker wire. Each gauge number lower cuts the resistance by about 20% (so 12 to 10 AWG cuts it by about 37%), and every three gauge numbers halves it. Sizes above 4 AWG are 3, 2, 1, then 1/0, 2/0, 3/0 and 4/0 ("four-ought").

Electrical work can start fires and cause serious injury or death. Use this for planning and learning, follow your local electrical code, and have a licensed electrician do or inspect household wiring.

Frequently asked questions