Kinetic Energy Calculator
Calculate the energy of a moving object, or the speed for a given energy.
Please note: Results use idealised models — point masses, no air resistance, ideal gases and uniform materials. Real experiments deviate. Use these for study and estimation, not for engineering sign-off.
What the Kinetic Energy Calculator does
Kinetic energy is the work needed to accelerate a mass from rest to its current speed, and the energy it will release when stopped. Because velocity is squared, energy climbs far faster than speed — the single most important fact about impact severity.
Formula
KE = ½ × m × v²v = √(2 × KE ÷ m)m = 2 × KE ÷ v²
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Solve for | one of 3 options | Yes | — |
| Mass | number | In some modes | Shown Solve for is Kinetic energy, or Solve for is Velocity. |
| Mass unit | one of 6 options | In some modes | Shown Solve for is Kinetic energy, or Solve for is Velocity. |
| Velocity | number | In some modes | Shown Solve for is Kinetic energy, or Solve for is Mass. |
| Velocity unit | one of 5 options | In some modes | Shown Solve for is Kinetic energy, or Solve for is Mass. |
| Kinetic energy | number | In some modes | Shown Solve for is Velocity, or Solve for is Mass. |
| Kinetic energy unit | one of 8 options | In some modes | Shown Solve for is Velocity, or Solve for is Mass. |
| Gravitational acceleration | m/s² | Optional | Standard gravity on Earth is 9.80665 m/s². The Moon is 1.62, Mars 3.72. Accepts 0 or more. |
How to use it
- Choose Solve for.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Gravitational acceleration.
- Select Calculate.
Worked example
A 1,200 kg car travelling at 100 km/h.
- Mass
- 1200 kg
- Velocity
- 100 km/h
100 km/h is 27.7778 m/s. KE = ½ × 1200 × 27.7778² = 462,963 J, or 463 kJ — the same energy as dropping the car from 39.3 m.
Frequently asked questions
Why is speed squared in the formula?
Because the work done accelerating an object rises with both the force applied and the distance over which it acts, and a faster object covers more distance in the same time. The two effects compound into a square.
What does the equivalent drop height mean?
The height a fall would need to give the same energy. A 100 km/h crash carries the energy of dropping the car off a twelve-storey building.