Kinetic Energy Calculator
This kinetic energy calculator solves the classic physics formula KE = ½mv² in seconds, giving you the energy of any moving object from its mass and velocity. It is built for students, teachers, and anyone who needs a fast, accurate answer without rearranging equations by hand.
Because velocity is squared in the formula, doubling an object's speed quadruples its kinetic energy — the reason high-speed collisions are so much more destructive than slow ones. The tool also runs the math in reverse, so you can solve for mass or velocity when you already know the energy, and read the result in your choice of units.
How to Calculate Kinetic Energy
Choose what to solve for
Use the three tabs to pick Energy (KE = ½mv²), Mass (m = 2KE/v²), or Velocity (v = √(2KE/m)). The calculator rearranges the formula and shows only the inputs it still needs.
Enter the known values
Type your two known figures and pick a unit from the dropdown beside each field. You can mix systems freely — for example, mass in pounds and velocity in mph — and the tool handles every conversion.
Read the result instantly
The answer updates in real time as you type — there is no submit button. The main result appears in your chosen unit, ready to copy or compare.
Check the working
See the full formula with your actual values plugged in, expand the unit-conversion table to view the result in every unit, and (when solving for energy) compare it against real-world references on the bar chart.
Features
Three Solve Modes
Switch between solving for kinetic energy, mass, or velocity with a single tap — the formula and inputs adjust automatically.
Real-Time Calculation
Results update instantly as you type or change a unit. There is no submit button to press.
10 Energy Units
Work in Joules, kJ, MJ, calories, kilocalories, electron volts, BTU, foot-pounds, watt-hours, or kilowatt-hours.
7 Mass Units
Enter mass in kilograms, grams, milligrams, pounds, ounces, metric tons, or US tons.
5 Velocity Units
Choose meters per second, kilometers per hour, miles per hour, feet per second, or knots.
Step-by-Step Formula
See the exact equation with your own values substituted in, so the result is easy to verify and understand.
Unit Conversion Table
Expand one table to see your result expressed in every available unit at once, with your selected unit highlighted.
Energy Comparison Chart
When solving for energy, a bar chart compares your result with real-world references — from a tennis serve to a moving train.
Frequently Asked Questions
How do you calculate kinetic energy?
Use the formula KE = ½mv²: multiply half the mass (in kilograms) by the velocity (in meters per second) squared. In this calculator, pick the Energy tab, enter mass and velocity in any supported unit, and the kinetic energy appears instantly in Joules or your chosen energy unit.
What is the kinetic energy formula?
The formula is KE = ½mv², where KE is kinetic energy in Joules, m is mass in kilograms, and v is velocity in meters per second. It can be rearranged to find mass (m = 2KE/v²) or velocity (v = √(2KE/m)), and this tool handles all three forms.
How do I find velocity from kinetic energy and mass?
Rearrange the formula to v = √(2KE/m). Select the Velocity tab, enter the kinetic energy and the mass, and the calculator returns the speed in the velocity unit you choose. The same logic works for mass under the Mass tab.
Why is velocity squared in the formula?
Kinetic energy equals the work needed to accelerate an object to its speed, and that work grows with the square of velocity. So doubling the speed requires four times the energy — a car at 100 km/h carries about four times the kinetic energy of the same car at 50 km/h.
What unit is kinetic energy measured in?
The SI unit of kinetic energy is the Joule (J). This calculator also displays the result in kilojoules, megajoules, calories, kilocalories, electron volts, BTU, foot-pounds, watt-hours, and kilowatt-hours so you can use whichever fits your context.
Can kinetic energy be negative?
No. Mass is always positive and velocity is squared, so kinetic energy is always zero or positive. An object that is not moving has exactly zero kinetic energy.
Is the calculator accurate for very high speeds?
It uses the classical (Newtonian) formula, which is accurate for everyday speeds. For objects approaching the speed of light, relativistic effects become significant and a different equation would be required.
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