Quick answer
Power is P = W ÷ t or P = F v. Doing 5,000 J of work in 20 s is 250 W, which is 0.335 mechanical horsepower or 0.25 kW.
Choose a mode and enter work and time, or force and velocity. The calculator returns power in watts, horsepower and kilowatts.
Related tools: Power Converter: Convert watts, kilowatts, horsepower and BTU per hour. Power of 2 Calculator: Compute 2 raised to an integer power exactly. Wind Power Estimate Calculator: Power from a wind turbine rotor at a wind speed.
How to use the Power Calculator
- Choose use: Work ÷ time and Force × velocity.
- Optionally, enter work (J).
- Optionally, enter time (s) (above 0).
- Optionally, enter force (N).
- Optionally, enter velocity (m/s).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Use | Choose one: Work ÷ time; Force × velocity | Starts at Work ÷ time |
| Work (optional) | A number, in J | — |
| Time (optional) | A number, in s | > 0 |
| Force (optional) | A number, in N | — |
| Velocity (optional) | A number, in m/s | — |
Formula and method
Formula
P = W ÷ t = F v
IEEE-754 double precision; shown to the decimals indicated.
1 hp (mechanical) = 745.69987 W.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Use = Work ÷ time; Work = 5000; Time = 20.
| Result | Value |
|---|---|
| Power | 250 W |
| Horsepower (mechanical) | 0.335256 |
| Kilowatts | 0.25 |
Example 2
Inputs: Use = Force × velocity; Force = 250; Velocity = 4.
| Result | Value |
|---|---|
| Power | 1,000 W |
| Horsepower (mechanical) | 1.341022 |
| Kilowatts | 1 |
Example 3
Inputs: Use = Work ÷ time; Work = 746; Time = 1.
| Result | Value |
|---|---|
| Power | 746 W |
| Horsepower (mechanical) | 1.000402 |
| Kilowatts | 0.746 |
The first line is the headline result (power). Below it the power Calculator lists horsepower (mechanical) and kilowatts, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Worked example
5,000 ÷ 20 = 250 W. A force of 50 N moving at 5 m/s is also 250 W. 1 mechanical horsepower is 745.7 W, so 250 W = 0.3353 hp.
Everyday values
A person can sustain about 100 W for hours and 250 W cycling hard for an hour. A kettle is 2 to 3 kW. Only the fields for the chosen mode are used.
How the result changes with work
Holding every other input at the first worked example, this table changes only work. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Work | Power | Horsepower (mechanical) | Kilowatts |
|---|---|---|---|
| 2500 | 125 W | 0.167628 | 0.125 |
| 5000 | 250 W | 0.335256 | 0.25 |
| 10000 | 500 W | 0.670511 | 0.5 |
| 20000 | 1,000 W | 1.341022 | 1 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Time: left empty shows "Enter the time." beside that field and no result.
- Force: left empty shows "Enter the force." beside that field and no result.
Choosing between the Power Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Power Converter](/converters/power-converter/) | value, from and to | Horsepower (mechanical) → Watt (W) |
| [Power of 2 Calculator](/math/power-of-2/) | exponent n | 2^10 |
| [Wind Power Estimate Calculator](/science/wind-power-estimate-calculator/) | rotor diameter, wind speed and power coefficient | Power |
| [Potential Energy Calculator](/science/potential-energy-calculator/) | mass, height and gravitational acceleration | Potential energy |
| [Solar Panel Output Calculator](/science/solar-panel-output-calculator/) | panel rating, number of panels and peak sun hours per day | Energy |
Background: motion and mechanics
For constant acceleration the standard relations are v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t. Pick the equation that contains your three known quantities and the one you want. Use SI units (metres, seconds, kilograms, newtons, joules) throughout or the answer will be off by a factor.
These equations stop applying when acceleration changes during the motion, as with a rocket burning fuel; that needs calculus or numerical methods.
Assumptions and limitations
- Only the fields for the chosen mode are used
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for time and force to confirm this.
Frequently asked questions
What is a watt?
One joule per second.
How many watts in a horsepower?
745.7 for mechanical.
How do I get energy from power?
Energy = power × time: 250 W for 20 s is 5,000 J, and 1 kW for 1 hour is 3.6 MJ (1 kWh).
What does the Power Calculator calculate?
Mechanical power from work and time, or force and velocity. It returns Power, Horsepower (mechanical) and Kilowatts.
What formula does the Power Calculator use?
P = W ÷ t = F v. 1 hp (mechanical) = 745.69987 W.
What do I need to enter in the power Calculator?
You enter Use. Optional: Work (J), Time (s), Force (N) and Velocity (m/s).
What does the “Use” option change?
It sets how the power is worked out. The choices are Work ÷ time and Force × velocity.
What is an example of a power result?
With use Work ÷ time, work 5000 and time 20, the power is 250 W.
Related calculators
- Power Converter — Convert watts, kilowatts, horsepower and BTU per hour.
- Power of 2 Calculator — Compute 2 raised to an integer power exactly.
- Wind Power Estimate Calculator — Power from a wind turbine rotor at a wind speed.
- Potential Energy Calculator — Gravitational potential energy from mass, height and gravity.
- Solar Panel Output Calculator — Daily, monthly and yearly energy from a solar array.
- Solar Payback Calculator — Simple payback period of an installation after incentives.
Sources
- OpenStax, University Physics Volume 2 (Rice University): electricity, circuits and thermodynamics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.