Kinetic Energy Calculator
The kinetic energy calculator starts with a 1,500 kg car at 100 km/h. Change the mass and speed; the table shows what half, double and triple the speed would carry.
Kinetic energy
- Kinetic energy KE = ½mv² = ½ × 1,500 kg × (27.7778 m/s)² = 578,700 J.
- 578.7 kJ (578,700 J)
- The unit algebra A joule is a newton-meter, and a newton is kg·m/s², so a joule is kg·m²/s², exactly what mass times speed squared produces. The ½ comes from integrating force over distance from rest: W = ∫F dx = ∫mv dv = ½mv².
- kg·(m/s)² = kg·m²/s² = J
- In other units
- 578,700 J 578.7 kJ 138,300 cal 138.3 kcal 0.1608 kWh 426,800 ft-lbf
- Twice the speed would carry Four times the energy, because speed is squared. That is why stopping distance and crash damage grow so much faster than speed.
- 2,315 kJ (2,315,000 J)
- Same energy as a fall from v² / 2g: the height an object would have to drop, ignoring air, to reach this speed. Mass cancels, so this is true of anything moving at this speed.
- 39.34 m
- Momentum at this speed
- 41,670 kg·m/s
- Speed used
- 27.78 m/s 100 km/h 62.14 mph 91.13 ft/s
| Speed | Kinetic energy | Times the energy above |
|---|---|---|
| 50 km/h | 144.7 kJ (144,700 J) | 0.25× |
| 100 km/h | 578.7 kJ (578,700 J) | 1× |
| 150 km/h | 1,302 kJ (1,302,000 J) | 2.25× |
| 200 km/h | 2,315 kJ (2,315,000 J) | 4× |
| 300 km/h | 5,208 kJ (5,208,000 J) | 9× |
- Results are shown to four significant figures. Round to the precision of your least precise measurement.
How the Force Calculator works
KE = ½mv². Kinetic energy is half the mass times the speed squared. With mass in kilograms and speed in meters per second, the answer is in joules.
Worked example, the one above: a 1,500 kg car at 100 km/h. Convert the speed first: 100 km/h is 27.78 m/s. Then KE = ½ × 1,500 × 27.78² = 578,700 J (to four figures), or 578.7 kJ. That is the energy the brakes have to turn into heat to stop it, and about the energy of the same car dropped from 39.3 m, the height that gives 100 km/h in free fall.
The square is the whole story. Double the speed and the kinetic energy quadruples; triple it and it rises ninefold. The table under the result shows it. At 50 km/h the car carries a quarter of the energy it does at 100. This is why braking distance grows roughly with the square of speed and why a modest rise in speed makes a collision so much worse: the energy to be absorbed rises far faster than the speed.
Where the ½ comes from. Push a mass from rest with a constant force F over a distance d. The work done is Fd. The force is ma, and the kinematics equation v² = 2ad gives d = v² / 2a, so the work is ma × v² / 2a = ½mv². Kinetic energy is exactly the work it took to get the object up to speed, and the work it will do on whatever stops it.
Units. kg × (m/s)² = kg·m²/s², which is a newton (kg·m/s²) times a meter: a joule. If the speed is entered in km/h or mph it must be converted to m/s before squaring, or the answer is off by a factor of 3.6² = 12.96 or 2.237² = 5.0. The calculator converts first and shows the speed it used.
Kinetic energy is not momentum. Both depend on mass and speed, but momentum, mv, is linear in speed and has a direction, while kinetic energy is quadratic and has none. In a collision momentum is always conserved; kinetic energy usually is not. Some becomes heat, sound and bent metal.
Speed is measured relative to something, and so is kinetic energy. The figure here is relative to the ground, or whatever frame the speed was measured in. And ½mv² is the classical form; above a few percent of the speed of light it understates the energy.
Force Calculator FAQ
What is the formula for kinetic energy?
KE = ½mv², half the mass times the speed squared. A 1,500 kg car at 27.78 m/s (100 km/h) has ½ × 1,500 × 27.78² = 578.7 kJ. Use kilograms and meters per second to get joules.
What happens to kinetic energy when speed doubles?
It quadruples, because speed is squared. A car at 100 km/h carries four times the kinetic energy it has at 50 km/h, which is why stopping distances and crash forces rise so steeply with speed.
How do I find speed from kinetic energy?
Rearrange to v = √(2KE / m). A 1,500 kg car with 578.7 kJ is moving at √(2 × 578,700 / 1,500) = 27.78 m/s, which is 100 km/h.
More from the Force Calculator
Sources
- NASA NSSDCA Moon Fact Sheet, bulk parameters table, row "Surface gravity (m/s2)", Moon column (page last updated January 11, 2024) (2026)
- NASA NSSDCA Mars Fact Sheet, bulk parameters table, row "Surface gravity (mean) (m/s2)", Mars column (page last updated May 19, 2025) (2026)