Kinetic Energy CalculatorSolve KE = ½mv² for energy, mass or velocity in any units
Get the energy of anything that moves, compare it with cars, bullets and sprinters, and see why doubling speed quadruples the energy.
By Manzoor Ahmad, web development expert · Updated How do you calculate kinetic energy?
Use KE = ½mv², with mass in kilograms and speed in meters per second, to get joules. A 1,500 kg car at 100 km/h (27.78 m/s) has KE = 0.5 × 1,500 × 27.78² ≈ 579,000 J (579 kJ). Because speed is squared, the same car at 50 km/h has only a quarter of that energy.
Compared with everyday objects (log scale)
Kinetic energy formula, rearranged
Work in SI units (kg, m/s) to get joules. The calculator converts km/h, mph, pounds and tonnes for you. At speeds above about 1% of the speed of light it switches to the relativistic form, KE = (γ − 1)mc².
Worked examples
1. A car at highway speed
1,500 kg at 100 km/h: v = 100 ÷ 3.6 = 27.78 m/s. KE = 0.5 × 1,500 × 771.6 = 578.7 kJ, the same speed it would reach after falling about 39 m.
2. Speed from energy
A 2.0 kg object has 100 J of kinetic energy: v = √(2 × 100 ÷ 2.0) = 10 m/s.
3. Why speeding matters
At 50 km/h the same car has 144.7 kJ; at 130 km/h it has 978 kJ. Going 2.6 times faster means 6.8 times more energy for the brakes, or a crash, to absorb.
Kinetic energy of everyday objects
| Object | Mass | Speed | Kinetic energy |
|---|---|---|---|
| Raindrop falling | 0.03 g | 9 m/s | 1.2 mJ |
| Baseball pitch | 145 g | 40 m/s (144 km/h) | 116 J |
| 9 mm pistol bullet | 8 g | 360 m/s | 518 J |
| Sprinter at top speed | 80 kg | 10 m/s | 4.0 kJ |
| Car on the highway | 1,500 kg | 100 km/h | 579 kJ |
| Loaded truck | 40 t | 90 km/h | 12.5 MJ |
Kinetic energy FAQs
Kinetic energy is KE = ½mv², where m is mass in kilograms and v is speed in meters per second. The result is in joules (J).
Square the speed, multiply by the mass, then halve it. A 1,500 kg car at 100 km/h (27.78 m/s) has KE = 0.5 × 1,500 × 27.78² = 578,700 J, or about 579 kJ.
It quadruples, because KE depends on speed squared. A car at 100 km/h carries four times the energy it has at 50 km/h, which is why stopping distances grow so quickly with speed.
Rearrange to v = √(2KE ÷ m). An object of 2 kg with 100 J of kinetic energy moves at √(200 ÷ 2) = 10 m/s.
Rearrange to m = 2KE ÷ v². If an object moving at 5 m/s has 250 J of kinetic energy, its mass is 2 × 250 ÷ 25 = 20 kg.
The SI unit is the joule: 1 J = 1 kg·m²/s². Other units include kilojoules, calories (1 cal = 4.184 J), kilowatt-hours (3.6 MJ), foot-pounds and electronvolts.
No. Mass is positive and speed squared is never negative, so kinetic energy is always zero or positive.
It is the height you would have to fall from, without air resistance, to reach the same speed: h = v² ÷ 2g. A car at 100 km/h has the same speed as one dropped from about 39 m, roughly a 13-storey building.
Kinetic energy (½mv²) is a scalar that measures the energy of motion. Momentum (mv) is a vector that measures quantity of motion and is conserved in all collisions, while kinetic energy is conserved only in elastic ones.
Above roughly 1% of the speed of light (about 3,000 km/s), ½mv² starts to underestimate the true energy. The correct formula is KE = (γ − 1)mc², which this calculator applies automatically at those speeds.
Total energy is always conserved, but kinetic energy can be converted into heat, sound and deformation. In a car crash most kinetic energy ends up as crushed metal and heat.
A 9 mm pistol bullet of about 8 g at 360 m/s has roughly 500 J. That is far less than a moving car, but concentrated on a tiny area.
Sources
This kinetic energy calculator is for education. Crash, ballistic and safety engineering require full analysis beyond simple kinetic energy figures.