Electrical calculators that show their math

Size wire, check voltage drop, size the ground wire, fill conduit and convert watts, amps and VA. Every result shows the formula and the NEC table it came from.

CalculatorWhat it works out
Voltage Drop CalculatorVolts lost, percent drop and load voltage for DC or AC runs.
Wire Size CalculatorSmallest AWG for your amps and distance, AC or DC.
Conduit Fill CalculatorFill percent and max wires for EMT and PVC.
Watts to Amps CalculatorConvert power to current for any circuit type.
Amps to Watts CalculatorConvert current to power, with kVA.
Ground Wire Size CalculatorGround wire size by breaker rating, per NEC 250.122.
VA to Watts CalculatorVA to watts and back, using power factor.

Guides & charts

Which calculator do I need?

Start with the wire size calculator when you know the load and the run length. It checks ampacity and voltage drop together. Use the voltage drop calculator to test a wire you already have, and the conduit fill calculator to see how many conductors fit in a raceway. The ground wire size calculator applies NEC Table 250.122, and the watts to amps, amps to watts and VA to watts calculators convert power and current. Below you will also find charts for wire gauge, 12V DC wire size, breaker wire size and conduit fill.

A note on codes

These tools follow the NEC tables most US jurisdictions adopt, but local amendments, terminal temperature ratings and derating for bundled or hot conductors can change the answer. Treat results as a starting point and confirm with your inspector or a licensed electrician.