About this tool
The Kinetic Energy Calculator is a free, in-browser physics tool that applies KE = ½mv² and solves for whichever of the three quantities — energy, mass, or velocity — you leave blank. Velocity can be entered in metres per second, kilometres per hour, miles per hour, or feet per second, and it is converted to SI units before the calculation.
All arithmetic happens locally in your browser with no network calls, so your inputs never leave your device. Leave exactly one field empty and the calculator fills it in live as you type, and it also reports the object's linear momentum p = mv as a bonus.
Kinetic energy is expressed in joules (J), mass in kilograms (kg), and the underlying velocity in metres per second (m/s). The constant ½ is exact; the only approximations are the unit-conversion factors (1 km/h = 1/3.6 m/s, 1 mph = 0.44704 m/s, 1 ft/s = 0.3048 m/s).