Kinetic Energy Calculator
Find kinetic energy from mass and velocity, or solve for either.
About the Kinetic Energy Calculator
Kinetic energy is the energy of motion. It grows with the square of speed: doubling speed quadruples the energy, which is why braking distances rise so quickly and why a small rise in speed makes crashes much worse.
Enter mass and speed to find the energy, or solve for mass or speed. The answer is also shown in kilojoules and kilocalories. This is the classical formula, accurate well below the speed of light.
The formula
KE = ½ m v²
- KE
- kinetic energy, in joules (J)
- m
- mass, in kilograms (kg)
- v
- speed, in metres per second (m/s)
Worked example
A 1,500 kg car at 100 km/h and at 50 km/h
- 100 km/h = 27.78 m/s: KE = ½ × 1,500 × 27.78² ≈ 578,700 J
- 50 km/h = 13.89 m/s: KE ≈ 144,700 J
- Half the speed, a quarter of the energy the brakes must absorb
Questions people ask
Why does speed matter so much?
Energy depends on v², so 100 km/h has 4× the energy of 50 km/h.
What unit is a joule?
1 J = 1 kg·m²/s².