Power Calculator - Calculate Power (P = W/t) | Free Online Tool

A power calculator (also called a P = W/t calculator) is an online tool that computes power using the fundamental physics equation P = W/t, where P is power (in watts), W is work done (in joules), and t is time (in seconds). This formula is one of the cornerstones of classical mechanics and electrical engineering. Power is the rate at which work is done or energy is transferred. In simpler terms, it measures how quickly energy is used or produced.

Power calculations are essential in physics, engineering, and everyday life. For example, a 100-watt light bulb consumes 100 joules of electrical energy every second. An electric motor's power rating tells you how much mechanical work it can perform per second. Human power output, the power of a car engine, and the energy consumption of household appliances are all expressed in watts (or horsepower).

This free online power tool operates entirely within your browser - no data is sent to any server, ensuring your privacy and enabling offline use. It supports 6 work units (J, kJ, cal, kcal, Wh, kWh), 5 time units (s, min, h, ms, μs), and 5 power output units (W, kW, mW, hp, BTU/h), with automatic unit conversion. Whether you are a student solving physics homework, an engineer calculating motor power, or a homeowner estimating energy costs, this calculator is your go‑to solution.

Using this power and time calculator is simple. Follow these steps:

1. Enter the work value in the first input field.
2. Select the work unit from the dropdown (J, kJ, cal, kcal, Wh, kWh).
3. Enter the time value in the second input field.
4. Select the time unit from the dropdown (s, min, h, ms, μs).
5. The power is automatically calculated as you type.
6. Select your desired power unit from the output dropdown (W, kW, mW, hp, BTU/h).
7. Copy the result using the copy button, or use Clear All to reset.

The power formula is derived from the definition of work. Work is the energy transferred when a force moves an object over a distance. Power measures how quickly that energy transfer occurs. If you lift a heavy box slowly, you do the same amount of work as lifting it quickly, but the power output is lower because the work takes more time.

The formula can be rearranged to solve for any variable:

• Power: P = W / t
• Work: W = P × t
• Time: t = W / P

• Completely free, no registration. Unlimited calculations with no hidden costs.
• Privacy‑first design. All calculations happen locally in your browser. Your data never leaves your device.
• Supports 6 work units, 5 time units, and 5 power units - covering both metric and imperial measurement systems.
• High precision with results to 6 decimal places, suitable for educational, engineering, and scientific applications.
• Works offline after initial page load.
• Fully responsive design with resizable panels on desktop for custom workflow.