Kinetic Energy Calculator

Calculate the energy of a moving object

Last updated: 10/8/2026

Kinetic energy is the energy an object has because it is moving: the work it took to bring it up to speed, and the work it can do when it stops. Enter a mass in kilograms and a speed in metres per second and the calculator returns the translational kinetic energy in joules, kilojoules, and calories. Because speed is squared, small speed changes have outsized effects, which is why the formula matters for everything from braking distances to ballistics.

Calculator Inputs

Mass (kg)*

Velocity (m/s)*

Results

Enter values above to see your results

The calculator gives classical translational kinetic energy only; it does not include rotational energy or relativistic corrections.

How It Works

KE = ½ × m × v², with m in kilograms and v in metres per second, giving joules (1 J = 1 kg·m²/s²). Kilojoules are joules ÷ 1,000. The calorie shown is the thermochemical calorie (1 cal = 4.184 J), not the dietary kilocalorie; divide by a further 1,000 for food Calories. To use other units, convert first: km/h ÷ 3.6 = m/s, mph × 0.44704 = m/s, lb × 0.453592 = kg.

Why speed matters more than mass

Kinetic energy is linear in mass but quadratic in speed. A car at 100 km/h has four times the kinetic energy it has at 50 km/h, and stopping it requires the brakes to absorb four times the energy; on the road that shows up as a braking distance that roughly quadruples. The same logic explains why wind turbines produce eight times more power when wind speed doubles (energy per unit mass goes up fourfold, and twice as much air arrives per second).

What this formula does not include

The result is translational kinetic energy only. A spinning object also has rotational kinetic energy (½ I ω²), which matters for wheels, flywheels, and thrown balls. The formula is also the classical, low-speed version: at speeds approaching a few percent of the speed of light the relativistic form is needed, but for any everyday object the difference is immeasurable.

Worked example

Default inputs: 70 kg at 10 m/s (a sprinter near top speed)

Square the speed:10²= 100 m²/s²

Kinetic energy:½ × 70 × 100= 3,500 J (3.5 kJ)

In calories:3,500 × 0.239006= 836.5 cal (0.84 food Calories)

A 1,500 kg car at 100 km/h

Convert speed:100 ÷ 3.6= 27.78 m/s

Kinetic energy:½ × 1,500 × 27.78²= 578,700 J ≈ 579 kJ

Compare at 50 km/h:½ × 1,500 × 13.89²= 144,700 J, one quarter as much

Tips & Best Practices

•Doubling the mass doubles the energy; doubling the speed quadruples it.
•Enter speed in m/s. For km/h divide by 3.6; for mph multiply by 0.447.
•Kinetic energy is a scalar: direction does not matter, and it is never negative.

Frequently Asked Questions

What is a joule?

The joule is the SI unit of energy: the work done by a force of one newton over one metre. Lifting a small apple (about 100 g) one metre takes roughly 1 J. A 60 W bulb uses 60 J every second.

Why is the calorie value so small compared with food labels?

The calculator shows thermochemical calories (4.184 J each). Food labels use kilocalories, written "Calories" or kcal, which are 1,000 times larger. The 3,500 J default is 836.5 cal but only 0.84 kcal.

Is kinetic energy the same as momentum?

No. Momentum is m × v, a vector proportional to speed; kinetic energy is ½ m v², a scalar proportional to speed squared. Two objects can have equal momentum and very different kinetic energies, which is why a light fast object can do more damage than a heavy slow one with the same momentum.