---
title: "Energy and power calculator — free, runs in your browser"
description: "Kinetic and potential energy, work, power, and what they cost in electricity. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/energy-power-calculator/
site: "At One Place"
---

# Energy and power calculator

Kinetic and potential energy, work, power, and what they cost in electricity.

## How it works

Calculates kinetic energy, gravitational potential energy, work and power, and converts the result into kilowatt-hours and a running cost.

Kinetic energy scales with the square of speed, and that single fact explains most of road safety. Doubling speed quadruples the energy that has to be dissipated in a crash, and roughly quadruples the braking distance. A car at 60 km/h carries four times the energy it does at 30, not twice.

Potential energy is mgh, which makes the numbers involved in lifting things surprisingly small compared with heating them. Lifting a 70 kg person ten metres takes about 6,900 joules — less than two watt-hours, and about a thousandth of what boiling a kettle uses.

Power is energy per unit time. A joule per second is a watt, and a kilowatt-hour is 3.6 million joules.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### Why does speed matter so much in a crash?

Kinetic energy is proportional to velocity squared. Doubling speed quadruples the energy that has to go somewhere.

### How many joules in a kilowatt-hour?

3,600,000. A kilowatt for an hour is 1,000 joules per second for 3,600 seconds.

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## Sources

- Calculated on this page — At One Place (/about/)