Kinetic Energy Calculator
Find the kinetic energy of a moving object from its mass and velocity, using KE = ½mv².
The formula
KE = ½ × mass (kg) × velocity² (m/s)², giving energy in joules. Kinetic energy grows with the square of velocity, so doubling speed quadruples the kinetic energy for the same mass.
Worked example
A 1,000 kg car travelling at 20 m/s (about 72 km/h) has a kinetic energy of ½ × 1,000 × 20² = ½ × 1,000 × 400 = 200,000 J (200 kJ).
Why speed matters more than weight for impact energy
Because velocity is squared in the formula, a relatively small increase in speed has a much bigger effect on kinetic energy than the same percentage increase in mass — this is why stopping distances and impact forces increase so sharply at higher speeds.
Frequently asked questions
What units does velocity need to be in?
Meters per second (m/s) for the formula to give an answer in joules directly. If your speed is in km/h or mph, convert it to m/s first using the Unit Converter.
Does this account for air resistance or friction?
No — this calculates the theoretical kinetic energy of an object based purely on its mass and velocity at one instant, not any energy lost to drag, friction, or other real-world forces over time.