Watt Calculator
Watts measure the rate at which electrical energy is used or produced. The formula is simple: multiply volts by amps to get watts. A standard US outlet at 120V supplying 10 amps delivers 1,200 watts. This calculator also converts your result to kilowatts, horsepower, and BTU per hour.
The formula:
P (watts) = V (volts) × I (amps)
This is the most fundamental equation in electrical work. If you know the voltage of your power source and the current your device draws, you can find exactly how much power it consumes.
Common examples:
- A 60W light bulb on a 120V circuit draws 0.5 amps
- A 1,500W space heater on 120V draws 12.5 amps
- A 240V dryer pulling 25 amps uses 6,000 watts (6 kW)
Unit conversions:
- 1 kilowatt (kW) = 1,000 watts
- 1 mechanical horsepower (HP) = 745.7 watts
- 1 watt = 3.412 BTU/hr
Kilowatts are what your electric utility uses for billing. Horsepower shows up on motors and engines. BTU per hour is common in HVAC sizing.