Kinetic Energy Calculator
Calculate kinetic energy
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Working out how to calculate kinetic energy is easier with Kinetic Energy Calculator, which answers as you type. Drop Mass (kg) and Velocity (m/s) into Kinetic Energy — the figure refreshes as you type. The answer from Kinetic Energy arrives with its working attached. Use Kinetic Energy for a reliable number, fast. Kinetic Energy runs in your browser. Science data stays in the tab. Looking for kinetic energy calculator or free online kinetic energy calculator? Kinetic Energy covers both. The labels in Kinetic Energy match the terms in its result. Kinetic Energy stays bookmarked for next time.
What the defaults give
A 5 kg mass at 10 m/s has 250 joules of kinetic energy.
Velocity is squared in the formula, so doubling speed quadruples the energy while doubling mass only doubles it. That asymmetry is the reason speed limits matter more than vehicle weight in crash severity.
The formula
KE = ½ × m × v², with mass in kilograms, velocity in metres per second and energy in joules.
v² = 100, so KE = 0.5 × 5 × 100 = 250 J.
Worked example
Mass 5 kg
Velocity 10 m/s
v² = 100
KE = ½ × 5 × 100 = 250 J
What 250 joules means
It is the energy needed to lift 25 kg by one metre, or roughly the impact of dropping a 2.5 kg object from 10 m. For comparison, a 1,500 kg car at 13.9 m/s (50 km/h) carries about 145,000 J — nearly 600 times as much, which is why vehicle mass and speed scale consequences so sharply.
Where people go wrong
- Using km/h. The formula needs m/s; 10 km/h is 2.78 m/s, not 10. Entering km/h overstates the energy by a factor of 12.96.
- Squaring after multiplying. The square applies to velocity alone, not to ½mv.
- Confusing momentum with energy. Momentum is mv (linear in velocity); kinetic energy is ½mv². They answer different questions.
- Ignoring rotation. A rolling ball also carries rotational energy, ½Iω², which this calculation omits.
Related quantities
Work done to reach this speed equals the kinetic energy gained, so a constant 50 N force over 5 m delivers 250 J. Stopping distance follows the same curve: at twice the speed you need four times the energy and, at the same braking force, four times the distance.
Frequently Asked Questions
Why is 5 kg at 10 m/s 250 J?
KE = ½mv², so 0.5 × 5 × 100 = 250 joules. The velocity is squared before multiplying by mass.
What happens if I double the speed?
The energy quadruples, because velocity is squared. Doubling mass only doubles the energy — the two inputs are not equivalent.
What units should I use?
Kilograms and metres per second, giving joules. Convert km/h to m/s by dividing by 3.6 — 36 km/h is 10 m/s.
Is kinetic energy the same as momentum?
No. Momentum is mass × velocity and is linear; kinetic energy is ½mv² and is quadratic. A heavy slow object can have high momentum and modest energy.
Does a rolling object have more energy?
Yes — it also carries rotational kinetic energy, ½Iω². For a solid sphere that adds about 40% to the translational figure.
What is the kinetic energy at 100 km/h for a 1,500 kg car?
Convert first: 100 km/h is 27.8 m/s. Then ½ × 1,500 × 27.8² = 579,000 J, or 579 kJ. That is roughly 2,300 times the 250 J in the default example, which is why speed dominates crash energy.
What is the kinetic energy of a 70 kg person running at 3 m/s?
0.5 x 70 x 9 = 315 J. Doubling the speed to 6 m/s gives 1,260 J — four times as much — which is the arithmetic behind the difference between a jog and a sprint impact.
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