Wire size calculator

How it works

The tool works out the load current and picks the smallest copper conductor that meets both ampacity and the voltage drop limit. In imperial mode it uses NEC Table 310.16 (60 °C column) and the small-conductor rule; metric mode follows IEC values.

How to measure

Add up the wattage on the appliance labels. Measure cable length one way from the panel to the load.

Tips

• Continuous loads (3 hours or more) should not exceed 80% of the breaker rating.
• The breaker must not be larger than the wire is rated for.
• Motors, multi-wire branch circuits and long feeders need a licensed electrician.