Kinetic Energy Calculator
By Santaji GadepatilinUpdated October 27, 2026
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Type in any field to change it. Press × on a value to calculate that field instead.
Kinetic energy (kJ) vs Speed (km/h) — other inputs held at your current values.
How to use this calculator
Enter mass and speed to get the kinetic energy, or enter the energy to find the speed. Units convert automatically (km/h, mph, m/s; J, kJ, kWh).
The formula
KE = ½ m v²
Worked example
A 1,200 kg car at 100 km/h (27.78 m/s):
KE = 0.5 × 1,200 × 27.78² = 463 kJ
At 50 km/h the same car has only 116 kJ — one quarter.
Speed and safety
| Speed | Kinetic energy (1,200 kg car) |
|---|---|
| 30 km/h | 42 kJ |
| 50 km/h | 116 kJ |
| 80 km/h | 296 kJ |
| 120 km/h | 667 kJ |
This is why small speed increases make crashes much more severe.
Frequently asked questions
What is the kinetic energy formula?
KE = ½ × m × v², with mass in kg and speed in m/s giving energy in joules.
Why does speed matter so much?
Energy depends on the square of speed. Doubling speed means four times the energy — and roughly four times the braking distance.
Where does kinetic energy go when a car brakes?
Mostly into heat in the brakes. Electric and hybrid cars recover part of it with regenerative braking.