Kinetic Energy Calculator
Enter any two of kinetic energy, mass and speed to get the third — joules, kilojoules, kWh or calories; kg or pounds; m/s, km/h or mph.
Answer
E = ½ × m × v²
- Given (in base units): m = 1,500 kg, v = 27.7778 m/s
- E = ½ × m × v² = 578,704 J
Values
Fill in any 2; leave the one to work out empty.
How is this calculated?
E = ½ × m × v², so m = 2E ÷ v² and v = √(2E ÷ m).Runs in your browser — nothing you enter leaves this device.
About this tool
What it does
Kinetic Energy Calculator works out the energy a moving object carries because of its motion: half its mass times the square of its speed. Enter any two of energy, mass and speed and the third is worked out, with the formula and the working shown in SI units. Each field has its own unit — energy in joules, kilojoules, megajoules, watt-hours, kilowatt-hours, calories, kilocalories or electronvolts; mass in kilograms, grams, tonnes or pounds; speed in metres per second, kilometres per hour, miles per hour, feet per second or knots — so you can ask questions the way they come up: how much energy a car at 100 km/h has, how fast a cricket ball must travel to carry a given energy, or how much energy braking turns into heat. The page opens with a 1,500 kg car at 100 km/h, which carries about 579 kJ.
How to use it
- Type two of the three values and pick their units.
- Leave the third empty; it is worked out straight away and highlighted.
- Switch the answer’s unit to compare, for example kilojoules or kilowatt-hours.
- Read the working under the answer to check each step.
Limits and your data
- This is the energy of motion in a straight line. A spinning wheel or ball also has rotational energy, which this does not include.
- Speed is relative: the same car has a different kinetic energy measured from the road and from another moving car. Use the speed relative to whatever it might hit or stop against.
- Because energy grows with the square of speed, doubling the speed quadruples the energy — and the braking distance. Small changes in speed matter a lot.
- At more than about a tenth of the speed of light, ½mv² is no longer accurate; the page says so when your numbers get there.
- Results are shown to six significant figures; real inputs are rarely that precise.
- The calculation runs in your browser. Nothing you enter is sent or saved.
Questions
Why does speed matter more than mass?
Because it is squared. A car at 60 km/h has four times the kinetic energy it has at 30 km/h, but a car twice as heavy at the same speed has only twice the energy.
How much energy does a car have at highway speed?
A 1,500 kg car at 100 km/h carries about 579 kJ — roughly the energy of lifting it 39 metres. All of it has to be turned into heat by the brakes to stop.
How do I find speed from kinetic energy?
Enter the energy and the mass and leave speed empty: v = √(2E ÷ m). 100 J in a 0.16 kg cricket ball is a speed of about 35 m/s, or 127 km/h.
What is the difference between kinetic and potential energy?
Kinetic energy comes from motion; potential energy from position, such as height above the ground. A falling object turns one into the other.