⚡ Power Calculator (P = W/t)
Find power as work divided by time (P = W/t), or solve for the work done or the time taken.
Power P
50 W
Power P = W / t (work ÷ time). Also P = F·v (force × velocity). 1 watt = 1 J/s. 🔒 Computed in your browser.
How the power calculator (p = w/t) works
Power is the rate of doing work: P = W/t, measured in watts (1 W = 1 J/s). Enter any two of power, work and time and the tool solves for the third. Power can also be written P = F·v (force times velocity). Because work is energy transferred, power equally means energy ÷ time, so a 100 W device uses 100 J every second however the energy is delivered.
Power is about how fast energy is transferred, not how much. Cross-link: convert between watts and horsepower in the unit converters.
Frequently asked questions
How do I calculate power?
Divide work (or energy) by time: P = W/t. Doing 1000 J in 20 s is 50 W. Enter work and time to compute power.
What is a watt?
The SI unit of power: 1 watt = 1 joule per second. A 60 W bulb uses 60 J of energy every second.
What is the difference between energy and power?
Energy (joules) is the total work done; power (watts) is how quickly it is done. The same job done faster requires more power.
What is P = Fv?
An equivalent form: power equals force times velocity. It’s handy when a constant force moves something at a steady speed, such as a car engine overcoming drag.
How do I convert watts to horsepower?
1 mechanical horsepower ≈ 745.7 watts. Use the power unit converter for exact conversions.
Worked example: climbing stairs
A 70 kg person climbing 3 m in 4 s does work W = mgh = 70 × 9.81 × 3 ≈ 2060 J, at a power of P = W/t ≈ 515 W, roughly two-thirds of a horsepower.
When do I use P = Fv?
When a steady force moves something at constant speed. For a car overcoming 500 N of drag at 30 m/s, the engine delivers P = 500 × 30 = 15,000 W (about 20 hp) just to hold that speed.
What is a kilowatt-hour?
An energy unit, not a power unit: one kilowatt (1000 W) sustained for one hour, equal to 3.6 million joules. Electricity bills use it because power (kW) times time (h) gives the energy consumed.
Do two machines doing the same work have the same power?
Not necessarily. Two hoists lifting the same load to the same height do equal work, but the faster one, finishing in less time, has the greater power output, since power is work divided by time.