About this calculator
Watts measure how fast a load consumes energy. Amps measure current flow. Convert between them using voltage and power factor. This calculator handles single-phase and three-phase loads and outputs results in watts (use the Amps to kW tool for kilowatt outputs).
Formula
Watts equals volts times amps for DC and resistive single-phase loads. Add a power factor multiplier for inductive AC loads. Three-phase adds √3.
Single-phase: W = V × I × PF
Three-phase: W = √3 × V × I × PF
How to use
- Pick single-phase or three-phase.
- Enter current in amps and voltage.
- Enter power factor (1.0 for resistive, lower for motors).
- Read the result in watts.
Worked example
Setup
A 120 V single-phase LED light strip draws 0.5 A with a power factor of 0.9.
Calculation
W = 120 × 0.5 × 0.9 = 54 W.
Answer
The strip consumes 54 watts of real power.
Frequently asked questions
- When can I skip the power factor?
- For purely resistive loads (heating elements, incandescent lamps), PF = 1.0 and W = V × I. Skip the PF input or set it to 1.0. For any load with a motor, transformer, or switching power supply, PF matters and should be included.
- Does this give peak or RMS watts?
- RMS. Both the voltage and current inputs are RMS values, so the resulting power is the average real power - which is what bills, breakers, and equipment ratings are based on.
- How do I find the power factor of my load?
- Check the nameplate first - many motors and electronic loads list it. Otherwise, measure it with a power quality meter or use typical values: 0.85-0.90 for general motors, 0.95+ for modern LED drivers, 1.0 for resistive heat.