What is kinetic energy?
Kinetic energy is the energy an object possesses because of its motion. It is defined by the formula KE = ½mv², where m is mass in kilograms and v is velocity in metres per second. The result is expressed in joules (J). Because velocity is squared, doubling an object's speed quadruples its kinetic energy—a fact with profound implications for vehicle safety, engineering design, and sports science.
How to use this calculator
Choose what you want to find—Energy, Mass, or Velocity—with the toggle. Enter the two known values and click Calculate. The result card displays the answer, the applied formula, and a plain-language interpretation. When solving for energy, you also get conversions to kilojoules, calories, kilocalories, watt-hours, electronvolts, foot-pounds, and BTU. When solving for velocity, speed conversions (m/s, km/h, mph) appear automatically.
Rearranging the formula
From the base equation you can derive m = 2·KE / v² (find mass) and v = √(2·KE / m) (find velocity). The calculator handles the algebra automatically—select the unknown and enter the other two values. No manual rearrangement needed.
Practical applications
Automotive engineers calculate the kinetic energy a car carries at highway speed to design crumple zones and braking systems. Ballistics experts use KE to assess projectile impact energy. Sports scientists measure the kinetic energy of a sprinting athlete or a struck ball. Physicists apply the concept to particles in accelerators, where masses are tiny but speeds approach the speed of light (relativistic corrections apply at such extremes).
Tips
Use consistent SI units (kg and m/s) to get the answer in joules directly. Remember that KE is always positive or zero—it cannot be negative. For rotating objects, use rotational kinetic energy (KE = ½Iω²) instead. This free calculator runs entirely in your browser with no sign-up, no download, and instant results on any device. Bookmark it for quick kinetic-energy calculations whenever you need them.