Kinetic Energy Calculator

Enter the mass and speed of a moving object to find its kinetic energy.

This result is an estimate only. Double-check important figures before relying on them.

How it is calculated

Kinetic energy (joules) = ½ × mass (kg) × speed² (m/s)²
If you enter km/h, the speed is divided by 3.6 first
1 kilojoule = 1,000 joules

For stored energy from height, use the potential energy calculator. For motion over time, see the speed, distance and time calculator.

Worked example

A 1,000 kg car at 20 m/s (72 km/h):

KE = ½ × 1,000 × 20² = 200,000 J, which is 200 kJ

At 40 m/s the energy is four times as much: 800 kJ.

Why your number may differ

This is the energy of straight-line motion only. It does not include the spinning energy of wheels or the energy lost to air and friction. Relativistic effects are ignored, which is fine at everyday speeds.

Frequently asked questions

What is the formula for kinetic energy?

Kinetic energy = ½ × mass × speed². With mass in kilograms and speed in metres per second, the answer is in joules.

Why does speed matter so much?

Speed is squared. Doubling the speed makes the energy four times larger, which is why crashes at higher speed are so much more severe.

How do I convert km/h to m/s?

Divide by 3.6. A car at 72 km/h moves at 20 m/s.