Kinetic Energy Calculator

What is kinetic energy?

Every moving object carries energy because of its motion. This is kinetic energy, and it depends on mass and on the square of speed: E = ½ × m × v². With mass in kilograms and speed in metres per second the result is in joules.

Why the square of speed matters

Speed enters the formula squared. Doubling the speed gives four times the kinetic energy. This is why a car at 100 km/h needs roughly four times the braking distance of one at 50 km/h: the brakes have four times as much energy to turn into heat.

Example

A 1200 kg car travels at 90 km/h. First convert the speed to SI units: 90 / 3.6 = 25 m/s. The kinetic energy is 0.5 × 1200 × 25² = 375 000 J, or 375 kJ.

Working backwards

With energy and mass known, speed is v = √(2 × E / m). With energy and speed known, mass is m = 2 × E / v². The calculator has a separate tab for each.

Limits

The formula is for an object moving in a straight line. A spinning wheel or flywheel has rotational energy as well. At very high speeds (close to the speed of light) the classical formula no longer holds.