Find the energy of motion. This free kinetic energy calculator solves for energy, velocity or mass using KE = ½mv², accepts m/s, km/h or mph, and shows joules, kilojoules, calories and watt-hours.
Solve for
joules
kg
Enter the two known values. Mass is in kilograms; velocity can be m/s, km/h or mph and is converted to m/s internally. Energy is in joules.
Kinetic energy
—
Enter two values
Joules
—
Kilojoules
—
Calories
—
Watt-hours
—
Kinetic energy is the energy of motion: KE = ½ × m × v². Because velocity is squared, doubling speed quadruples the energy — which is why speed matters so much for impacts.
Use this free kinetic energy calculator to find the energy of a moving object, or solve for its velocity or mass. It uses KE = ½ × m × v² and accepts m/s, km/h or mph.
What this kinetic energy calculator does
A kinetic energy calculator works out the energy of motion. Choose what to solve for — energy, velocity or mass — enter the other two, and it returns the result in joules, kilojoules, calories and watt-hours.
The kinetic energy formula
KE = ½ × m × v²
v = √(2·KE / m) m = 2·KE / v²
A 1000 kg car at 20 m/s (72 km/h) has 200,000 J (200 kJ) of kinetic energy.
Why speed matters so much
Speed
KE (1000 kg car)
10 m/s
50,000 J
20 m/s
200,000 J
30 m/s
450,000 J
40 m/s
800,000 J
Because velocity is squared, doubling speed quadruples energy — a key reason stopping distances and crash forces rise sharply with speed.
Units of energy
The SI unit is the joule (J). The calculator also shows kilojoules, calories (1 cal = 4.184 J) and watt-hours (1 Wh = 3600 J) for comparison.
How to use the kinetic energy calculator
Choose energy, velocity or mass to solve for.
Enter the other two values (pick a speed unit).
Read the result in several energy units.
Kinetic Energy FAQ
How do I calculate kinetic energy?
Use KE = ½ × m × v². For example, a 1000 kg car at 20 m/s has ½ × 1000 × 20² = 200,000 joules.
How do I find velocity from kinetic energy?
Rearrange to v = √(2·KE / m). The calculator does this when you solve for velocity.
Why does doubling speed quadruple the energy?
Because velocity is squared in the formula. Doubling v multiplies v² by four, so the kinetic energy is four times greater.
What units does it use?
Mass in kilograms and velocity in m/s, km/h or mph. Energy is shown in joules, kilojoules, calories and watt-hours.
What is kinetic energy?
It’s the energy an object has because it’s moving. A heavier or faster object carries more kinetic energy.
Is the kinetic energy calculator free?
Yes, this kinetic energy calculator is completely free, needs no sign-up, and gives instant results in your browser.
