Kinetic Energy Calculator
Give this calculator any two of mass, velocity and kinetic energy and it rearranges KE = 1/2 m v^2 to find the third. It works in SI units, so mass is in kilograms, velocity in metres per second and energy in joules. A 2 kg object moving at 3 m/s, for example, carries 9 joules of kinetic energy.
How to calculate kinetic energy
- Open the 'Solve for' menu and pick Kinetic energy, Velocity, or Mass, the quantity you want to find.
- Two input rows appear for the values you already know, one for each remaining quantity.
- Type the known mass in kg, velocity in m/s, or kinetic energy in J into those rows.
- Read the three result cards below; the one you solved for is highlighted.
- Click Copy to grab all three lines as plain text.
Examples
Energy from mass and velocity
Solve for Kinetic energy, mass 2 kg, velocity 3 m/s
Kinetic energy = 9 J
Velocity from mass and energy
Solve for Velocity, mass 2 kg, kinetic energy 9 J
Velocity = 3 m/s
Mass from velocity and energy
Solve for Mass, velocity 3 m/s, kinetic energy 9 J
Mass = 2 kg
Frequently asked questions
What is the kinetic energy formula?
Kinetic energy is one half times mass times velocity squared: KE = 1/2 m v^2. Energy comes out in joules when mass is in kilograms and velocity is in metres per second.
How do I find velocity from kinetic energy?
The calculator rearranges the formula to v = sqrt(2 times KE divided by m). The answer is the speed magnitude, so it is always zero or positive, never signed.
How do I find mass from kinetic energy?
It solves m = 2 times KE divided by v squared. Velocity must not be zero here, otherwise the mass is undefined and the tool shows an error instead of a number.
Why is energy the same for negative velocity?
Kinetic energy depends on velocity squared, so -3 m/s and +3 m/s give the identical 9 J. Direction is discarded, which is why KE tracks speed rather than velocity.
Can kinetic energy be negative?
No. With a positive mass and a squared velocity the result is always zero or positive, so the calculator rejects any negative energy you try to enter.
What units do I have to use?
SI units only: kilograms, metres per second and joules. Convert other units first, for example grams to kilograms or km/h to m/s, or the numbers will not line up with the formula.
Does it handle relativistic or rotational energy?
No. It uses the classical translational formula 1/2 m v^2, which is accurate for everyday speeds. It does not cover near light speed motion or the rotational energy of spinning bodies.
How precise are the results?
Each value is rounded to nine decimal places, so 9 stays 9 and long decimals are trimmed cleanly. That is far finer than most physics homework or lab work needs.
Is my calculation private?
Yes. Everything runs in your browser with no server call, so the masses, speeds and energies you enter never leave your device.
Learn more
- The kinetic energy formula KE = 1/2 m v squared
What the kinetic energy equation means, how to rearrange it for mass and velocity, and why doubling speed quadruples the energy of motion.
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