Kinetic Energy Calculator
Enter a mass and a speed to get the kinetic energy in joules — plus the momentum — and see why energy climbs with the square of velocity.
Energy and momentum at once
Enter the mass and velocity and the calculator returns the kinetic energy (½mv²) in joules and the momentum (mv) in kg·m/s together.
Use SI units
Mass in kilograms and velocity in metres per second give energy in joules — divide km/h by 3.6 to get m/s before you start.
What is kinetic energy?
The energy of motion
Kinetic energy is the energy an object has because it is moving. Any object with mass that is in motion carries it, and it grows with both how heavy the object is and — far more steeply — how fast it travels. The kinetic energy calculator turns two measurements, the mass in kilograms and the velocity in metres per second, into the energy in joules, alongside the momentum (mass times velocity). It is the number behind vehicle crash forces, the punch of a thrown ball, and the stopping power needed to bring a moving body to rest.
Enter a mass in kilograms and a speed in metres per second to get the kinetic energy in joules and the momentum instantly.
Kinetic energy is half the mass multiplied by the velocity squared, and momentum is simply mass times velocity.
KE = ½ × m × v²The velocity is squared, so it dominates the result: a small change in speed produces a large change in energy. Momentum (p = m × v) keeps speed to the first power, so it rises more gently. Use kilograms and metres per second and the energy comes back in joules and the momentum in kg·m/s.
Suppose a 1000 kg car is travelling at 20 m/s (about 72 km/h).
Square the velocity
20² = 400 — the squared speed that drives the energy.
Multiply by the mass
1000 × 400 = 400,000 — mass times velocity squared.
Take half
½ × 400,000 = 200,000 J (200 kJ) — the kinetic energy. The momentum is 1000 × 20 = 20,000 kg·m/s.
The two outputs answer two different questions. The kinetic energy (200,000 J for the car above) is how much work it would take to bring the object to a stop — the energy a brake, a wall, or a crumple zone must absorb. The momentum (20,000 kg·m/s) is how hard it is to change the object's motion and is what stays conserved in a collision. The crucial insight is that energy scales with the square of velocity: double the speed from 20 to 40 m/s and the kinetic energy jumps fourfold, from 200,000 to 800,000 J, while the momentum only doubles. That is exactly why stopping distance grows so fast with speed, why high-speed crashes are far more destructive than the speed increase alone suggests, and why a faster pitch or bullet delivers disproportionately more energy on impact. Heavier objects matter too, but only in direct proportion — speed is the lever that moves the result the most.
The formula is exact, but a couple of practical points are worth keeping in mind.
Translational motion and consistent units
This calculator gives the translational kinetic energy of an object moving in a straight line. It does not include rotational energy (a spinning wheel) or relativistic effects, which only matter near the speed of light. Keep your units consistent — kilograms for mass and metres per second for velocity — or the joules will be wrong: convert km/h to m/s by dividing by 3.6 before you enter the speed.