Wire Gauge Calculator
Estimate the wire gauge (AWG) needed for a circuit. The calculator checks both the wire’s current rating and the voltage drop over the length of the run.
How to use the Wire Gauge Calculator
- Enter the load current in amps.
- Enter the one-way length of the wire run and the circuit voltage.
- Choose copper or aluminum and the maximum voltage drop (3% is typical).
How it works
Two things limit wire size. Ampacity is how much current a wire can carry without overheating; small conductors are also limited by their breaker (14 AWG copper → 15 A, 12 AWG → 20 A, 10 AWG → 30 A). Voltage drop grows with length: VD = 2 × length × current × resistance per foot. Long runs often need a thicker wire than ampacity alone suggests. The NEC recommends keeping branch-circuit drop to about 3%.
This is a planning estimate. Insulation type, temperature, bundling and local codes all affect the required size — have electrical work checked by a licensed electrician.
Common copper wire sizes
| AWG | Typical breaker | Common use |
|---|---|---|
| 14 | 15 A | Lighting and general outlets |
| 12 | 20 A | Kitchen, bathroom and garage outlets |
| 10 | 30 A | Water heaters, dryers, window AC |
| 8 | 40–50 A | Ranges, large AC units |
| 6 | 50–60 A | EV chargers, subpanels |
| 4 | 70–85 A | Subpanels, large feeders |
Frequently asked questions
What size wire for a 20 amp circuit?
12 AWG copper for typical runs. For long runs (over about 75–100 ft at 120 V) go up to 10 AWG to limit voltage drop.
What size wire for 30 amps?
10 AWG copper, or 8 AWG aluminum.
What wire size for a 50 amp EV charger?
6 AWG copper is common, depending on insulation type and run length.
Does aluminum wire need to be bigger?
Yes — aluminum has about 64% more resistance than copper, so it is usually one or two sizes larger.