Breaker & wire size calculator
Find the correct breaker, conductor and ground size for an electrical circuit. Enter the load and conductor type to get sizes based on the NEC ampacity tables and the continuous-load rule.
How it works
- Applies the 125% continuous-load factor where it applies.
- Picks the next standard breaker size at or above the required current.
- Sizes copper and aluminum conductors and the equipment ground from NEC tables.
What changes your result
- The load current and whether it's continuous (the 125% rule)
- Conductor material — copper versus aluminium
- Terminal temperature rating (60°C vs 75°C)
- Derating for high ambient heat or bundled conductors
Frequently asked questions
What size wire do I need for a 50 amp breaker?
On 75°C copper, a 50-amp circuit typically uses 6 AWG conductors with a 10 AWG ground; aluminum goes up a size to 4 AWG. Always confirm terminal temperature ratings and any derating for your install.
What is the 80% rule for breakers?
A continuous load running three hours or more must not exceed 80% of the breaker rating. In practice you size the breaker and wire to at least 125% of the continuous current, which this calculator does automatically.
Can I use aluminum wire instead of copper?
Yes, where permitted, but aluminum carries less current per size, so you generally go up one or two gauge sizes versus copper. Use listed connectors and anti-oxidant where required. This calculator shows both.