Wire Gauge Calculator — AWG for Voltage Drop

How the wire gauge calculator works

Circular mils = (2 × K × amps × one-way distance) ÷ allowable voltage drop, where K = 12.9 for copper. Then pick the smallest AWG with at least that many CM.

Frequently asked questions

What wire size for a 20 amp circuit?

12 AWG copper up to ~50 ft on 120 V; for longer runs step up to 10 AWG to keep voltage drop under 3%.

Why does distance matter?

Longer runs multiply resistance, dropping voltage. NEC recommends keeping branch-circuit drop under 3%.

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