AC Wattage Calculator
Estimate the real power (in watts) drawn by an AC electrical circuit from its voltage, current, and power factor.
What this calculator does
It converts AC voltage and current readings into real electrical power (watts), which is what you’re typically billed for and what determines heating and energy use.
The formula
For a single-phase circuit, real power equals voltage times current times the power factor: P = V × I × PF. For a balanced three-phase circuit, P = √3 × V × I × PF. The power factor (between 0 and 1) accounts for the phase difference between voltage and current caused by inductive or capacitive loads; purely resistive loads like heaters have a power factor near 1.
This tool is for general electrical planning and education. For circuit sizing, wiring, or safety decisions, consult a qualified electrician and local electrical code.