Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate power from work done and time taken.
20.0000 W
Power measures how quickly work is done -- the same amount of work done faster means more power. This tool calculates power from work and time.
Enter work (joules) and time (seconds). Power appears instantly in watts (W).
Power = Work / Time
The result tells you the average rate at which energy was transferred over the time period you entered. It is an average: a machine might spend the first second doing most of the work and the rest coasting, but dividing total joules by total seconds smooths that out. If you need peak power rather than average power, you need a shorter time window that captures only the burst.
Imagine a hypothetical 20 kg box lifted straight up 3 m in 6 seconds. First find the work. The weight force is about 20 × 9.81 = 196.2 N, and the work is 196.2 × 3 = 588.6 J (you can compute this with the Work/Energy Calculator). Now enter 588.6 as the work and 6 as the time. The calculator returns 98.1 W. Divide by 746 to compare with horsepower, as the page suggests: 98.1 / 746 is about 0.13 hp. If the same lift took 3 seconds instead, the power would double to 196.2 W, even though the work is identical. This is the whole point of the quantity: same job, faster, more power.
The tool accepts negative work values, which give a negative power. Physically that describes energy being removed from a system, for example a brake absorbing kinetic energy, so it is meaningful in some contexts but may simply indicate a sign mistake in others. Results are rounded to four decimal places on screen. Very small times can produce enormous wattages; that is mathematically correct but you should question whether your time measurement is realistic.
Power comparisons are useful when sizing a motor, comparing how quickly two people or machines complete the same task, checking a student physics problem, or understanding why a small electric heater and a small lamp draw very different loads. Combine it with the Work/Energy Calculator to go from force and distance all the way to watts, or with the Kinetic Energy Calculator to estimate the power needed to accelerate an object to a given speed over a given time. For anything safety-critical, such as choosing a hoist or a motor for a real installation, use the manufacturer's ratings and consult a qualified engineer rather than relying on a simple average-power estimate.
The SI unit of power -- one watt equals one joule of work done per second.
1 horsepower ≈ 746 watts -- divide watts by 746 to convert.
Power is work divided by time, and dividing by zero is undefined. The tool therefore shows no result for a time of zero or less.
It is average power over the whole time you entered. Instantaneous power at a specific moment requires knowing the force and velocity at that instant.
Divide by 1,000. For example, 1,500 W is 1.5 kW. Multiplying kilowatts by hours gives kilowatt-hours.
You can if you know the energy in joules and the time in seconds, but appliances are normally rated directly in watts on their labels, which is the value you would use instead.
Reference: NIST Weights and Measures