Wire Size Calculator
Get a recommended wire gauge (AWG) for a given load in amps, for copper or aluminum, as a planning starting point before you check the code.
What your result means
Recommended wire size is the smallest standard AWG conductor whose ampacity meets your load, for the material you chose. Rated for is that conductor's ampacity. This is a starting point — a real circuit also factors in temperature, bundling, breaker rules, and voltage drop on long runs. Check drop with our voltage drop calculator, and convert a wattage load to amps first with the watts to amps calculator.
How to use this calculator
- Enter the circuit's load (or breaker size) in amps.
- Choose copper or aluminum.
- Read the recommended gauge and its ampacity.
- For long runs, check voltage drop and size up if needed.
- Verify everything against the NEC and local code before wiring.
The formula
Each wire gauge has an ampacity — the current it can safely carry. The calculator picks the smallest gauge that covers your load. Aluminum carries less than copper for the same size, so it needs a larger conductor.
Worked example
A 30 A copper circuit (a typical electric dryer) needs at least 10 AWG, which is rated for 30 A. In aluminum, the same 30 A load steps up to 8 AWG, because aluminum carries less current per gauge than copper.
Common wire sizes (copper)
| Load | Copper AWG | Typical circuit |
|---|---|---|
| 15 A | 14 AWG | Lighting, receptacles |
| 20 A | 12 AWG | Kitchen, bath, garage |
| 30 A | 10 AWG | Dryer, water heater, AC |
| 50 A | 8 AWG | Range, EV charger, subpanel |
| 100 A | 3 AWG | Subpanel feeder |
Tips & gotchas
- When in doubt, size up — a slightly larger wire runs cooler and drops less voltage.
- 14 AWG maxes at a 15 A breaker, 12 AWG at 20 A, and 10 AWG at 30 A.
- Aluminum needs anti-oxidant paste and listed terminations — not a DIY shortcut.
- Long runs often need the next size up to keep voltage drop under 3%.
- This is a planning estimate. The NEC and a licensed electrician have the final say.
Frequently asked questions
What size wire do I need for 30 amps?
10 AWG copper or 8 AWG aluminum for a typical 30 A circuit. Long runs may need a size larger to limit voltage drop.
What size wire for 50 amps?
8 AWG copper or 6 AWG aluminum is common for 50 A. Confirm the breaker, terminal temperature rating, and run length against the code.
Is copper or aluminum better?
Copper carries more current per gauge and is easier to terminate. Aluminum is cheaper for large feeders but needs larger wire and proper connectors.
Does wire length change the size?
It can. Short runs go by ampacity, but long runs may need a larger gauge to keep voltage drop within 3%. Check with the voltage drop calculator.
Can I wire a circuit from this?
Use it for planning only. Conductor sizing must follow the NEC, account for conditions of use, and ideally be done or checked by a licensed electrician.
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Estimates only — see our full disclaimer.