Wire Gauge Ampacity Calculator
Look up NEC-style copper wire ampacity (safe current capacity) by AWG size.
Ampacity
25 A
Covers copper conductors from 14 AWG to 4/0 AWG only, using NEC Table 310.16-style base ampacity values (30°C ambient, no more than 3 current-carrying conductors, no additional derating applied). Aluminum conductors have meaningfully lower ampacity at the same gauge and are not covered here — see the FAQ below.
Usage examples
Checking a residential branch circuit's wire size
Quickly look up a wire gauge suitable for a 20A circuit breaker against the NEC base table.
Sizing an extension cord or low-voltage run
Use the expected load current to pick a wire gauge with adequate headroom.
Comparing insulation temperature ratings
See how much ampacity the same wire gauge gains at a 90°C insulation rating versus 60°C.
Frequently asked questions
Can I use this directly for a real wiring installation?
This shows the NEC base ampacity table value, assuming 30°C ambient and no more than 3 current-carrying conductors. Real installations often need further derating for higher ambient temperatures or more bundled conductors, and must be verified by a qualified electrician against the full code — this tool is for quick reference, not a code-compliant installation calculation.
Does this support aluminum conductors?
No. Aluminum has meaningfully lower ampacity than copper at the same AWG size, and we didn't have confidence in a fully accurate aluminum table, so it's deliberately out of scope. Check NEC Table 310.16's aluminum column directly for that.
What happens if I pick a gauge outside the supported range?
The tool shows an out-of-range message instead of a guessed number. We'd rather narrow the range than show a value we're not confident in.