Wire size calculator

Enter the circuit. You get the gauge, the breaker and the voltage drop, with the rule behind each number.

The load

I know the

Current (A)

Voltage (V)

Runs 3 hours or more at a time

Heating, EV charging, lighting on all day. The Code makes you size for 125% of the load.

The run

One-way distance (ft)

From the panel to the device, not there and back. The calculator doubles it.

Termination rating

What the breaker and the device terminals are rated for, not the wire jacket. 60 degC is the safe assumption on most residential breakers.

Voltage drop limit

3% is the figure the Code recommends for a branch circuit. It is a recommendation, not a requirement.

Wire size by current and distance

Copper, 60 degC terminations, 240 V, 3% voltage drop limit. Read down to your current, across to your distance.

Load	25 ft	50 ft	75 ft	100 ft	150 ft	200 ft
15 A	14	14	14	12	12	10
20 A	12	12	12	12	10	8
30 A	10	10	10	10	8	6
40 A	8	8	8	8	6	6
50 A	6	6	6	6	6	4
60 A	4	4	4	4	4	4
100 A	1	1	1	1	1	1