Power Calculator

Power is the rate at which work is done or energy is transferred over time. It's calculated as P = W/t (work divided by time). Power is measured in Watts (W), where 1 Watt equals 1 Joule per second.

Energy is the total amount of work done or capacity to do work (measured in Joules). Power is how fast that energy is used or transferred (measured in Watts). A 100W bulb uses 100 Joules every second.

Horsepower (hp) is an older unit of power, originally comparing engines to horses. 1 hp = 745.7 Watts. It's still commonly used for engines and motors. A 200hp car engine produces about 149 kilowatts.

Multiply power (in kW) by time (in hours) to get energy in kWh (kilowatt-hours). Then multiply by your electricity rate. Example: 100W bulb for 10 hours = 1 kWh. At $0.12/kWh, that's $0.12.

Yes, when energy is being extracted rather than supplied. For example, regenerative braking in electric cars produces negative power (generates electricity). Generally, we focus on the magnitude.

kW (kilowatt) is power - the rate of energy use. kWh (kilowatt-hour) is energy - the total amount used over time. A 1kW heater running for 3 hours uses 3 kWh of energy.