← All tools/Calculators/Physics/Power Calculator
Power Calculator
Electrical or mechanical power — from work and time, or voltage and current.
Power
How it works
Mechanical: P = W ÷ t (watts = joules ÷ seconds) Electrical: P = V × I (watts = volts × amps) 1 kW = 1,000 W, 1 hp = 745.7 W
Worked example: 1,000 joules in 10 seconds is 1,000 ÷ 10 = 100 W, which is 0.10 kW and 100 ÷ 745.7 = 0.134 hp. A 230 V, 5 A appliance draws 230 × 5 = 1,150 W.
Frequently asked questions
What is the difference between watts and kilowatts?
Only scale: 1 kilowatt is 1,000 watts. Household bills use kilowatt-hours, which is power multiplied by time, not power itself.
What is a horsepower?
An older unit from the age of steam engines: 1 hp = 745.7 watts. Car engines are still quoted in hp in many countries, while motors are quoted in watts or kilowatts.
Does this work for AC as well as DC?
For resistive loads, yes — V × I gives the power. For AC motors and other reactive loads the real power is lower, so treat the result as an upper estimate.
More tools
Tell us what you think
Loving this tool, or stuck on something? Tell us — it takes a minute.
We’ll only use your name and email to reply if needed. The tool and page are filled in for you.