Electrical Calculators

Free online electrical calculators and sizing references for engineers, electricians, and students. Each tool comes with the formula, a worked example, and the relevant standard, so you can check the result rather than just trust it. Start with the groups below, or browse every tool underneath.

Cable Sizing and Conversion

Voltage Drop

Motor Calculators

Busway and Bus Duct

Clearance and Insulation

Quick Reference

Motor current (three-phase): I = P ÷ (√3 × V × power factor × efficiency), with P in watts and V as line voltage. Voltage drop: keep it low, because it matters most on long runs and low-voltage systems like 12V and 24V lighting or solar. The NEC informational notes suggest about 3% on a branch circuit and 5% overall, and other standards set their own limits. Always verify: calculators give an estimate, so confirm results against your local code and the manufacturer’s data before installing. For the code behind the numbers, see our Electrical Standards guides.

All Electrical Calculators