⚡Energy Calculator

About this tool

Choose kinetic energy, potential energy or unit conversion. Enter mass and speed, or mass and height, in metric or imperial units, and optionally a time to get average power in kilowatts and horsepower. Every result is converted into a table of energy units, from joules and kilojoules to calories, kilowatt-hours, BTU, foot-pounds and electronvolts.

How kinetic and potential energy are calculated

Kinetic energy, the energy of motion, is ½mv², with mass in kilograms and speed in metres per second giving joules. Because speed is squared, doubling speed quadruples the energy. A 1,000 kg car at 100 km/h, 27.8 m/s, carries about 386 kJ, while at 50 km/h it has only about 96 kJ. That energy has to be absorbed by the brakes, or in a crash, which is why stopping distances and injuries rise so steeply with speed. Gravitational potential energy near the Earth's surface is mgh, mass × 9.81 m/s² × height: lifting 1,000 kg by 10 metres stores about 98 kJ, which is the principle behind pumped-storage hydroelectric plants. Power is energy divided by time, so 386 kJ delivered in 10 seconds is an average of 38.6 kW, about 52 horsepower. Energy units vary by field: 1 kWh, the unit on electricity bills, equals 3.6 MJ, about 860 kcal or 3,412 BTU. Honest limits: these are the classical formulas, accurate for everyday speeds far below the speed of light, and potential energy assumes standard gravity near the surface. The SUVAT calculator solves motion problems, the electricity cost calculator prices kilowatt-hours and the unit converter handles other units.

Frequently asked questions