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Kinetic Energy Calculator

Find the kinetic energy and momentum of a moving object from its mass and speed.

By Nitin Raturi · Last reviewed

Your worksheet

How to use the Kinetic Energy Calculator

Find the energy and momentum of a moving object.

  1. Enter the mass in kilograms.
  2. Enter the speed and choose m/s or km/h.
  3. Read the kinetic energy, then the momentum and equivalents.

Good to know

  • Energy grows with the square of speed: twice as fast is four times the energy.

KE = ½ m v². Twice the speed means four times the energy.

Mass (kg)

How much matter is moving.

How to fill it in

  • Enter kilograms; 1 tonne is 1,000 kg and 1 g is 0.001 kg.

Example

A 0.145 kg ball at 40 m/s carries 116.00 J.

Speed

How fast it moves, in the unit you choose.

How to fill it in

  • Enter 0 to 10,00,000.

Example

A 1,000 kg car at 20 m/s has 2,00,000.00 J; at 40 m/s it has 8,00,000.00 J.

Speed unit

Metres per second or kilometres per hour.

How to fill it in

  • 1 km/h is 1,000 ÷ 3,600 m/s.

Example

A 1,500 kg car at 100 km/h has 5,78,703.70 J.

Kinetic energy

2,00,000.00 J

A 1,000 kg mass at 20 m/s carries 2,00,000.00 J of kinetic energy and 20,000.00 kg·m/s of momentum.

Speed in m/s
20.0000
Energy in joules
2,00,000.00
Energy in kilowatt-hours
0.055556
Momentum
20,000.00 kg·m/s
Same energy lifts it
20.39 m

KE = ½mv² and p = mv, classical mechanics (speeds far below light). 1 J = 1 kg·m²/s².

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

  1. Step 1Massm in kgHow much is moving.
  2. Step 2Speedv in m/skm/h are divided by 3.6.
  3. Step 3Energy½ m v²Work needed to reach that speed from rest.

Kinetic energy is the energy an object has because it moves. It equals the work needed to speed it up from rest, and the work needed to stop it again.

Momentum, m × v, is the related quantity that decides how hard a moving object is to stop in a given time.

Worked example: a 1,000 kg car at 20 m/s

Energy and momentum of a car at 72 km/h
KE
½ × m × v²
p
m × v
  1. Speed72 km/h ÷ 3.620 m/s
  2. Kinetic energy½ × 1,000 × 20²2,00,000.00 J
  3. Momentum1,000 × 2020,000.00 kg·m/s

That energy would lift the car 20.39 m straight up.

Read the result

  • 20 m/s (72 km/h)2,00,000.00 J
  • 40 m/s (144 km/h)8,00,000.00 J
Kinetic energy of a 1,000 kg car

Twice the speed means four times the energy, which is why braking distance grows so fast with speed.

  • Ball at 40 m/s116.00 JA 0.145 kg ball, about the mass of a cricket ball.
  • Car at 100 km/h5,78,703.70 JA 1,500 kg car on a highway.

Assumptions and limits

  • ClassicalValid far below the speed of light.
  • Translation onlySpin energy of wheels is not included.
  • FrameSpeed is measured relative to the ground.
  • No lossesFriction and drag are separate.

Kinetic energy depends on mass and speed squared, so doubling speed quadruples it.

For speed after constant acceleration, use the kinematics calculator. The projectile motion calculator follows a thrown object, and the horsepower calculator relates engine power to torque.

Common mistakes

  • Mistake: Using km/h directly in ½mv².

    Instead: Convert to m/s first, or choose km/h here.

  • Mistake: Thinking double speed doubles energy.

    Instead: It quadruples it; momentum doubles.

Checking the method

A separate script finds each energy as the work to reach that speed, integrating numerically instead of using ½mv².

Read how we test our calculators, or browse more maths calculators.

Frequently asked questions

What is the kinetic energy of a 1,000 kg car at 20 m/s?

2,00,000.00 J, from ½ × 1,000 × 20². Its momentum is 20,000.00 kg·m/s.

What happens to kinetic energy when speed doubles?

It quadruples: the same car at 40 m/s has 8,00,000.00 J.

How do I use km/h?

Choose km/h, or divide by 3.6 for m/s. A 1,500 kg car at 100 km/h has 5,78,703.70 J.

What is the difference between kinetic energy and momentum?

Energy (½mv², joules) grows with speed squared; momentum (mv) grows in proportion. A 0.145 kg ball at 40 m/s has 116.00 J and 5.80 kg·m/s.

Is this valid at very high speeds?

It is the classical formula, accurate far below the speed of light.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 4 Nov 2026; next review due by . Found an error? Tell us.

Changelog

  • : Initial release.