Power Calculator
Solve P = W ÷ t for power, work or time — enter the two values you have.
Reviewed by the OmniCalc teamMethod verified 2026-07-01
250W
= 0.25 kW
Power 250 WShow steps
- P = W ÷ t = 1,000 J ÷ 4 s = 250 W.
- In kilowatts: P = 250 W ÷ 1000 = 0.25 kW.
How to use the power calculator
- 1Choose to solve for power, work or time.
- 2Enter the two known values: work in joules (J) and time in seconds (s).
- 3Read the answer in watts, with the kilowatt equivalent and the rearranged formula under Show steps.
Power isn't energy
Work (joules) is the total energy spent; power(watts) is how fast you spend it. The same 1000 J delivered in 1 s is 1000 W, but over 100 s it’s only 10 W — same energy, different power. Your utility’skilowatt-hour is the reverse: it measures energy, not power.
Frequently asked questions
What is the power formula?
Power is the work done divided by the time taken: P = W ÷ t. Rearranged, work W = P × t and time t = W ÷ P. The result is in watts when work is in joules and time in seconds.
What is a watt?
One watt is one joule of energy transferred every second (1 W = 1 J/s). A 60 W bulb uses 60 joules each second; a 1500 W kettle uses 1500 joules each second, or 1.5 kilowatts.
How do watts relate to kilowatts?
A kilowatt is 1000 watts, so divide watts by 1000 to get kilowatts. The calculator shows the kilowatt equivalent automatically — 2500 W is 2.5 kW.
Why must time be greater than zero?
Power measures a rate over time, so dividing by zero (or a negative duration) has no physical meaning. Enter a positive number of seconds and the calculator returns a result.