Kinetic Energy Calculator
Kinetic energy is the energy an object carries because it is moving, set by its mass and the square of its speed. Enter mass and velocity to get the energy, or flip the calculator around to solve for the mass or speed when you already know the energy. You can switch units on every field and read the result in joules, calories, watt-hours or foot-pounds.
Formula
Worked example
2 kg at 3 m/s: KE = ½ × 2 × 3² = ½ × 2 × 9 = 9 J. In reverse, 9 J at 3 m/s gives m = 2 × 9 ÷ 9 = 2 kg.
How the calculation works
The calculator applies the classical kinetic energy formula from Newtonian mechanics, KE = ½mv², which ties energy to mass and to the square of velocity. Because velocity is squared, even a small change in speed produces a large change in energy. Internally every input is converted to SI base units (kilograms and metres per second) before the arithmetic, then the energy is reported in joules, the SI unit maintained by NIST, alongside everyday equivalents like calories and watt-hours.
Solving in reverse for mass or velocity
The same formula can be rearranged to find whichever quantity you are missing. Choose what you want to solve for and enter the other two values. To find mass from energy and speed, the tool uses m = 2·KE ÷ v². To find the speed needed to reach a given energy, it uses v = √(2·KE ÷ m). This is how engineers size flywheels, work out crash test impact speeds, or check the muzzle velocity needed for a target energy, all without rearranging the algebra by hand.
Units, momentum and energy equivalents
Mass can be entered in kilograms, grams, pounds, ounces or metric tonnes, and speed in metres per second, kilometres per hour, miles per hour or feet per second; the result reads in joules with conversions to kilojoules, calories, kilocalories, watt-hours and foot-pounds shown beside it. The calculator also reports linear momentum (p = m·v) in kilogram metres per second, since momentum and kinetic energy together describe a collision. Doubling the mass doubles both, but doubling the speed doubles momentum while quadrupling kinetic energy, which is why impact speed dominates collision severity.
Limitations to keep in mind
This is the classical, non-relativistic formula. It is accurate well below the speed of light and is fine up to roughly 1% of c (about 3,000 km/s); beyond that, relativistic corrections matter and you need a relativistic kinetic energy tool. The result is translational kinetic energy only: it ignores rotational energy (which depends on moment of inertia and spin), thermal energy and any potential energy. Results assume a rigid body or point mass moving with a single uniform velocity.
Everyday kinetic energy values
| Object | Mass | Speed | Kinetic energy |
|---|---|---|---|
| Falling raindrop | 0.0001 kg | 9 m/s | ~0.004 J |
| Thrown baseball | 0.145 kg | 40 m/s (90 mph) | ~116 J |
| Sprinting person | 70 kg | 10 m/s | ~3,500 J |
| Car on a highway | 1,500 kg | 30 m/s (108 km/h) | ~675,000 J |
| Bullet (rifle) | 0.004 kg | 900 m/s | ~1,620 J |
Approximate translational kinetic energy for familiar objects, rounded for scale.
Frequently asked questions
Can this calculator solve for mass or velocity, not just energy?
Yes. Use the solve-for selector to pick kinetic energy, mass or velocity, then enter the other two values. It rearranges KE = ½mv² for you: mass is m = 2·KE ÷ v² and velocity is v = √(2·KE ÷ m). This reverse mode is handy when you know a target energy and need the speed or mass that produces it.
Why does speed have a bigger effect on kinetic energy than mass does?
Speed enters the formula squared, so a 2x increase in speed yields a 4x increase in kinetic energy, while a 2x increase in mass yields only a 2x increase. This is why impact speed, not vehicle weight alone, is the dominant factor in collision severity, and why the calculator also shows momentum, which only doubles when speed doubles.
What units can I use, and what does the result mean?
Mass accepts kilograms, grams, pounds, ounces or tonnes, and speed accepts m/s, km/h, mph or ft/s. The primary result is in joules (J), defined as one kilogram times one metre squared per second squared (kg·m²/s²). For context, the tool also shows the energy in calories, watt-hours and foot-pounds; lifting a 100 g apple by one metre takes about one joule.
Can this formula be used for rotating objects?
Not directly. A rotating rigid body has rotational kinetic energy that depends on its moment of inertia and angular velocity, not just translational speed and mass. An object that both translates and spins, like a rolling ball, has a total kinetic energy equal to the sum of its translational part (from this calculator) and its rotational part.