Kinetic Energy Calculator
Calculate the kinetic energy of any moving object.
Enter mass and velocity to get energy in Joules, kilojoules, calories, and BTUs.
Supports metric and imperial units.
Kinetic energy is the energy that an object possesses because of its motion. Every moving object — from a thrown ball to a speeding car to an electron in an atom — carries kinetic energy. It is one of the two primary forms of mechanical energy (the other being potential energy).
The Kinetic Energy Formula
KE = ½ × m × v²
Where:
- KE = Kinetic energy (Joules, J)
- m = Mass of the object (kilograms, kg)
- v = Velocity of the object (meters per second, m/s)
Key Observations
- Kinetic energy increases with the square of velocity. Doubling speed quadruples kinetic energy.
- Kinetic energy increases linearly with mass. Doubling mass doubles kinetic energy.
- This is why vehicle speed is far more dangerous than vehicle mass in crash physics — a car at 100 km/h has 4× more kinetic energy than at 50 km/h.
Unit Conversions
| Unit | Relation to Joules |
|---|---|
| Joule (J) | Base unit |
| Kilojoule (kJ) | 1 kJ = 1,000 J |
| Calorie (cal) | 1 cal = 4.184 J |
| Kilocalorie (kcal) | 1 kcal = 4,184 J |
| BTU | 1 BTU = 1,055.06 J |
| Watt-hour (Wh) | 1 Wh = 3,600 J |
| Electron volt (eV) | 1 eV = 1.602 × 10⁻¹⁹ J |
Practical Examples
A 70 kg person running at 3 m/s (leisurely jog): KE = ½ × 70 × (3)² = ½ × 70 × 9 = 315 J
A 1,500 kg car at 100 km/h (27.78 m/s): KE = ½ × 1500 × (27.78)² = ½ × 1500 × 771.7 ≈ 578,775 J ≈ 579 kJ
A 9 mm bullet (8 g = 0.008 kg) at 370 m/s: KE = ½ × 0.008 × (370)² = ½ × 0.008 × 136,900 ≈ 547 J
Relation to Work
By the work-energy theorem, the net work done on an object equals its change in kinetic energy: W = ΔKE = ½m(v₂² − v₁²)
This relationship is fundamental to braking distance calculations — all of a vehicle’s kinetic energy must be dissipated as heat through the brakes to bring it to a stop.