Calculate the kinetic energy of a moving object with the formula KE = ½ · m · v². Enter any two of the three values — mass, velocity, and kinetic energy — leave the third blank, and the calculator solves for it. Units are converted automatically.
The kinetic energy calculator works out how much energy a moving object carries because of its motion. Whether it is a cricket ball hurled at 90 mph, a car speeding down a highway, or an electron whizzing through a wire, anything with mass that is moving has kinetic energy. This calculator uses the classic formula KE = ½ · m · v², and because it works in every direction, you can just as easily find the mass or the velocity when you know the energy. Enter any two values, leave the third blank, and get an accurate answer instantly, with flexible units throughout.
Kinetic energy is one of the foundational ideas in physics, tying together mass, speed, work, and the conservation of energy. This page explains what kinetic energy is, the formula behind the calculator, worked examples you can reproduce, how each variable is solved, real-world uses, and answers to the questions people ask most often.
Kinetic energy is the energy an object possesses because it is moving. The word comes from the Greek kinesis, meaning motion. Any object with mass that is in motion — from a subatomic particle to a planet — has kinetic energy, and the faster it moves or the more massive it is, the more energy it carries. An object at rest has zero kinetic energy; set it moving and it gains kinetic energy that can do work on other objects when it collides with or pushes them.
Kinetic energy is a scalar quantity, meaning it has magnitude but no direction — a car moving north and an identical car moving south at the same speed have exactly the same kinetic energy. It is measured in joules (J) in the SI system, the same unit used for all forms of energy, which reflects the deep principle that kinetic energy can be converted to and from other energy forms such as heat, sound, and gravitational potential energy.
The kinetic energy of an object is given by:
KE = ½ × m × v²
where:
The most important feature of this formula is that velocity is squared. This means kinetic energy grows far faster with speed than with mass. Double the mass and you double the kinetic energy; but double the speed and you quadruple it. Triple the speed and the energy increases ninefold. This squared relationship is why high speeds are so dangerous and why stopping distances grow so dramatically as vehicles go faster.
Consider a cricket ball with a mass of 165 g (0.165 kg) bowled at 90 mph. First convert the speed to m/s: 90 mph ≈ 40.23 m/s. Then apply the formula:
KE = ½ × 0.165 kg × (40.23 m/s)² ≈ 133.5 J
So the ball carries about 133.5 joules of kinetic energy — these are the calculator's default values, so you can press Calculate to see the result and then enter your own numbers.
A football (soccer ball) with a mass of 450 g kicked at 38.4 m/s has:
KE = ½ × 0.45 kg × (38.4 m/s)² ≈ 331.7 J
That is roughly 331.7 joules — more than double the cricket ball, thanks to its greater mass and speed.
Because the formula links three quantities, you can rearrange it to find whichever one you do not know. The calculator does this automatically — just leave one field blank:
This flexibility makes the tool useful for more than just finding energy. You can work out how fast an object must move to carry a given amount of energy, or deduce its mass from a measured energy and speed — handy in collision analysis, ballistics, and sports science.
The squared velocity term has profound real-world consequences. Because kinetic energy scales with the square of speed, a small increase in velocity produces a large increase in energy. A car travelling at 60 mph has four times the kinetic energy of the same car at 30 mph — not twice. This is exactly why a crash at highway speed is so much more destructive than a low-speed fender-bender, and why braking distances lengthen dramatically with speed: the brakes must dissipate all of that kinetic energy, and there is four times as much to get rid of at double the speed. The same principle explains why a fast-moving bullet, despite its tiny mass, carries enough energy to do serious damage, while a heavy object moving slowly may be relatively harmless.
Kinetic energy is intimately connected to the concept of work. The work-energy theorem states that the net work done on an object equals the change in its kinetic energy. In other words, to speed an object up you must do positive work on it, and that work becomes stored as kinetic energy; to slow it down, negative work is done, removing kinetic energy. This is why the formula uses the same unit — the joule — for both work and energy. When you push a stalled car and it starts rolling, the work of your push has been converted into the car's kinetic energy; when the brakes bring it to a halt, that kinetic energy is converted into heat in the brake pads.
Kinetic energy and potential energy are the two great categories of mechanical energy, and they constantly trade places. Potential energy is stored energy due to position or configuration — for example, gravitational potential energy from height. As an object falls, its potential energy decreases while its kinetic energy increases, so that (ignoring air resistance) the total mechanical energy stays constant. A roller-coaster car at the top of a hill has maximum potential energy and little kinetic energy; at the bottom it has maximum kinetic energy and minimal potential energy. This continual conversion, governed by the conservation of energy, is one of the most elegant and useful ideas in physics, and kinetic energy is one half of the story.
The SI unit of kinetic energy is the joule (J), which you get when mass is in kilograms and velocity in meters per second. For larger amounts, energy is often expressed in kilojoules (kJ) or megajoules (MJ). Other units the calculator supports include:
Because you can enter mass and velocity in everyday units and read the energy in whichever unit suits your context, the calculator removes the need for manual conversions.
Kinetic energy is often confused with momentum, but they are distinct. Momentum (p = m × v) is a vector that depends linearly on velocity and has direction, while kinetic energy (KE = ½ m v²) is a scalar that depends on the square of velocity and has no direction. Both are conserved in an isolated system, but they capture different aspects of motion. In an elastic collision, both momentum and kinetic energy are conserved; in an inelastic collision, momentum is conserved but some kinetic energy is converted into heat, sound, or deformation. Understanding the difference is essential for analyzing collisions, and this calculator focuses on the energy side of that picture.
The formula here describes translational kinetic energy — the energy of an object moving from one place to another, which is by far the most common case. But motion comes in other forms too. Rotational kinetic energy is the energy of a spinning object, such as a flywheel or a planet, and depends on its moment of inertia and angular speed. Vibrational kinetic energy arises from oscillating particles, and is central to understanding heat at the molecular level, since temperature is essentially a measure of the average kinetic energy of an object's particles. For everyday problems — balls, vehicles, projectiles — translational kinetic energy is what you want, and it is exactly what this calculator computes.
To build intuition, it helps to see the kinetic energy of familiar things. A 70 kg person jogging at 3 m/s carries about 315 joules; the same person sprinting at 8 m/s carries roughly 2,240 joules — more than seven times as much, from less than a threefold increase in speed, because of the squared velocity term. A 1,500 kg car at 30 mph (about 13.4 m/s) has around 135,000 joules of kinetic energy, while at 60 mph it has about 540,000 joules — four times more. A falling raindrop, a thrown baseball, and a bullet span an enormous range of energies despite their small masses, all governed by the same simple formula. Plugging your own everyday examples into the calculator is one of the best ways to develop a feel for just how quickly kinetic energy grows with speed.
The formula KE = ½ m v² is an excellent approximation for everyday speeds, but it is not the whole story. As an object's velocity approaches the speed of light, Einstein's special relativity takes over, and the true kinetic energy grows much faster than the classical formula predicts, heading toward infinity as the speed nears light speed. This is why no object with mass can ever reach the speed of light — it would require infinite energy. For any speed you are likely to deal with on Earth, even that of a fast jet or a spacecraft, the difference between the classical and relativistic results is negligible, so this calculator uses the standard non-relativistic formula, which is accurate to many decimal places at ordinary speeds.
KE = ½ × m × v², where m is mass in kilograms and v is velocity in meters per second. The result is in joules. Velocity is squared, so energy rises rapidly with speed.
Kinetic energy depends on the square of speed, so doubling the velocity quadruples the energy, and tripling it increases the energy ninefold. Speed matters far more than mass.
Yes. The calculator is bidirectional. To find velocity, use v = √(2·KE/m); to find mass, use m = 2·KE/v². Enter the two values you know and leave the unknown blank.
Kinetic energy is the energy of motion, while potential energy is stored energy due to position or configuration. As an object falls, potential energy converts into kinetic energy, keeping the total constant.
Kinetic energy is a scalar — it has magnitude but no direction. Two objects of the same mass moving at the same speed have equal kinetic energy regardless of the direction they travel.
The SI unit is the joule (J). The calculator can also display the result in kilojoules, megajoules, calories, kilocalories, watt-hours, kilowatt-hours, or foot-pounds.
This Kinetic Energy Calculator is provided for general educational and informational purposes. It computes translational kinetic energy using the standard formula KE = ½·m·v² and assumes speeds well below the speed of light (non-relativistic). For critical scientific or engineering work, verify results with appropriate methods.