About the Kinetic Energy Calculator
This kinetic energy calculator uses KE = ½ × m × v² to find the energy of a moving object, or works backwards to find its mass or speed from a known energy. Mass can be entered in kilograms, grams, pounds or tonnes, speed in m/s, km/h, mph or ft/s, and energy is reported in joules, kilojoules, calories, kilowatt-hours and foot-pounds.
It helps with physics homework, road-safety comparisons (why higher speeds are so much more dangerous), ballistics and sports science, and estimating how much energy brakes must dissipate. The chart shows how energy grows with the square of speed, so doubling your speed quadruples the energy.
The formula is the classical (non-relativistic) one, accurate for everyday speeds far below the speed of light. It gives translational kinetic energy only; rotational energy of spinning wheels or balls is not included.
How to use the kinetic energy calculator
- 1Choose whether to solve for energy, mass or velocity.
- 2Enter the two known values.
- 3Select units for mass, speed and energy.
- 4Read the answer, the conversions and the momentum.
- 5Use the chart to see how energy changes with speed.
Formula and method
Kinetic energy is the energy an object has because it is moving. It equals half the mass multiplied by the square of the velocity; with mass in kilograms and speed in metres per second the result is in joules (1 J = 1 kg·m²/s²). The calculator converts your units to SI, solves the chosen rearrangement and converts back.
Because speed is squared, energy rises much faster than speed: going from 50 to 100 km/h quadruples the energy a car’s brakes must absorb. The equivalent drop height, KE ÷ (m × g), is the height the object would have to fall from to reach the same speed.
- KE
- Kinetic energy (J)
- m
- Mass (kg)
- v
- Speed (m/s)
Worked examples
1,500 kg car at 100 km/h
100 km/h is 27.78 m/s. KE = ½ × 1,500 × 27.78² ≈ 578,704 J, or about 579 kJ — the energy the brakes must turn into heat to stop the car.
Baseball pitched at 90 mph
A 145 g baseball at 90 mph (40.23 m/s) carries ½ × 0.145 × 40.23² ≈ 117 J of kinetic energy.
Speed of a 70 kg runner with 3 kJ
v = √(2 × 3,000 J ÷ 70 kg) = √85.71 ≈ 9.26 m/s, about 33 km/h — a fast sprint for a recreational runner (elite sprinters peak above 40 km/h).
Frequently asked questions
What is the formula for kinetic energy?+
Kinetic energy equals one half times mass times velocity squared: KE = ½mv². Use kilograms and metres per second to get the answer in joules.
What happens to kinetic energy if speed doubles?+
It quadruples, because energy depends on the square of speed. Tripling the speed makes the kinetic energy nine times larger, which is why stopping distances grow so quickly with speed.
How do I find velocity from kinetic energy?+
Rearrange the formula: v = √(2 × KE ÷ m). For example 200 J on a 4 kg object gives v = √(100) = 10 m/s.
What is the difference between kinetic and potential energy?+
Kinetic energy is energy of motion (½mv²); gravitational potential energy is energy of position (mgh). A falling object converts potential energy into kinetic energy.
Is kinetic energy ever negative?+
No. Mass is positive and velocity is squared, so kinetic energy is always zero or positive regardless of the direction of motion.