About the Kinetic Energy Calculator
Kinetic energy is the energy an object has because it is moving. The faster and heavier it is, the more it has, and because speed is squared, doubling the speed makes the energy four times larger. This calculator takes the mass and the speed in the units you prefer and gives the energy in joules, kilojoules, watt-hours and food calories. Type the mass and the speed and the kinetic energy appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Kinetic Energy Calculator
- 1Enter the mass and the speed.
- 2Pick the units or options from the menus if the kinetic energy tool offers them.
- 3Read the kinetic energy in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the kinetic energy
Engineers use kinetic energy to size brakes, crash barriers and flywheels, because that is the energy which has to go somewhere when a moving object stops. Safety writers use it to explain why a collision at 100 km/h is far worse than one at 50 km/h: the energy is four times bigger, not twice.
Students meet the formula in physics classes, sports scientists use it to compare a thrown ball with a kicked one, and cyclists use it to see how much braking a long descent needs. The tool shows the answer in watt-hours too, so you can compare it with batteries.
How the kinetic energy is worked out
Kinetic energy = ½ × mass × speed², with the mass in kilograms and the speed in metres per second. A 1,000 kg car travelling at 100 km/h, which is 27.78 m/s, has ½ × 1,000 × 27.78² = 385,802 J, or about 386 kJ. At 200 km/h the same car has 1,543,210 J, four times as much.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Mass in kg or lb
- Speed in m/s, km/h or mph
- Also shows J, kJ, Wh and kcal
Mistakes to avoid with kinetic energy
The most common error is to mix units. A speed in km/h put straight into the formula gives an answer that is wrong by a factor of about 13, because the formula needs metres per second. Another is to forget that the speed is squared, which makes high speeds count for much more than low ones.
On phone and computer
On a phone, type into the boxes one after another and read the kinetic energy underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the kinetic energy move. The kinetic energy calculator works the same on both. Convert the answer with Energy Converter, find the speed with Speed Calculator, compare the stored energy with Potential Energy Calculator, and use Momentum Calculator for the mass-and-velocity view.
Features
- Double the speed, four times the energy
- Convert km/h to m/s by dividing by 3.6
- Energy is what brakes must absorb
- Clear messages when the kinetic energy inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate kinetic energy?
Kinetic energy = ½ × mass × speed², with the mass in kilograms and the speed in metres per second. A 1,000 kg car travelling at 100 km/h, which is 27.78 m/s, has ½ × 1,000 × 27.78² = 385,802 J, or about 386 kJ. At 200 km/h the same car has 1,543,210 J, four times as much.
What is the formula for kinetic energy?
Kinetic energy = ½ × mass × speed², with the mass in kilograms and the speed in metres per second. The kinetic energy calculator applies it exactly and rounds only the displayed answer to six significant figures.
Why does doubling the speed quadruple the energy?
Because kinetic energy depends on the square of the speed. Twice the speed gives 2² = 4 times the energy, and three times the speed gives nine times the energy.
Does kinetic energy depend on direction?
No. It is a scalar, so only the mass and the size of the speed matter, not the direction of travel.
How does kinetic energy compare with food calories?
One food calorie (kilocalorie) is 4,184 joules. The 386 kJ of a moving car is about 92 food calories of energy.
Is this kinetic energy calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.