Kinetic Energy Calculator
Kinetic energy calculator (KE = ½mv²): solve for energy, mass or velocity in SI units, with a US/imperial readout. Curriculum-aligned.
Kinetic Energy Calculator
Enter any two values and leave the third blank — the calculator solves for it. Results are in SI units, with a US/imperial readout below.
- Curriculum
- English (global) — Cambridge International + IB
- Built against
- Cambridge IGCSE Physics 0625 + IB Diploma (2023–2025) — Kinetic Energy
- Unit system
- SI primary; US/imperial readout below
- First published
- 2 Jun 2026
- Last updated
- 5 Sep 2026
View authoritative scientific sources
- NIST SP 811 (2008), §3 — units & conversions
- BIPM SI Brochure, 9th edition (2019)
- Kinetic energy — Encyclopædia Britannica
⚠️ Educational use only — see full disclaimer
EDUCATIONAL USE DISCLAIMER
This calculator is provided for educational and reference purposes only. It is not a substitute for instruction from a qualified teacher, your prescribed textbook, or your school's official curriculum materials.
When preparing for examinations, always cross-check our calculations and notation against your current syllabus and your teacher's guidance. Syllabus conventions and accepted notation vary between curricula and may change between examination years.
If you believe any calculation, notation, or curriculum reference in this tool is inaccurate, please let us know via the feedback button. We review feedback promptly and update tools when verified corrections are needed.
RECATOOLS accepts no liability for academic, examination, professional, or research outcomes arising from use of this tool.
How to Use the Kinetic Energy Calculator
Pick your curriculum
Use the curriculum pills above to match your syllabus (Cambridge/IB, 高考 or SPM). Terminology and the whole page follow your selection.
Enter any two values
Type two of kinetic energy, mass and velocity — leave the one you want to find blank. Each field has a unit selector.
Read the SI result
The answer is shown in SI units — joules (J), kilograms (kg), metres per second (m/s), with a dimmed US/imperial readout below.
Check against your syllabus
The Tool Information block shows exactly which syllabus this is built against. Spot something off? Use the feedback button.
Kinetic Energy, in Your Curriculum's Words
Kinetic Energy (KE = ½ × mass × velocity²)
Example: A ball of mass 2.0 kg moves at 3.0 m/s. Find its kinetic energy.
Given: m = 2.0 kg, v = 3.0 m/s. Using KE = ½mv²:
KE = ½ × 2.0 × 3.0² = 9.0 J
Kinetic energy is the energy an object has because of its motion: KE = ½mv². Energy is in joules (J), mass in kilograms (kg), velocity in metres per second (m/s) — the SI units every curriculum here teaches. Rearranged, the same relation gives mass (m = 2KE / v²) or velocity (v = √(2KE / m)), which is why this tool solves for whichever value you leave blank.
Because velocity is squared, doubling the velocity quadruples the kinetic energy — which is why speed matters so much in collisions. SI is always the primary result, with a dimmed US/imperial readout for reference. All calculation happens in your browser — nothing is uploaded.
Doubling a car's speed quadruples its kinetic energy — and the distance it needs to stop.
Double the speed and the energy quadruples
Kinetic energy is KE = ½mv², measured in joules (J).
Doubling the velocity quadruples the kinetic energy.
It is a scalar quantity — it has no direction.
Kinetic energy cannot be negative.
Work done on an object changes its kinetic energy.
For a spinning object, rotational KE is ½Iω².
One joule equals 1 kg·m²/s².
Kinetic energy depends on the observer's frame of reference.
In an elastic collision, total KE is conserved.
This calculator runs in your browser — your working stays private.
Frequently Asked Questions
- KE = ½mv² — kinetic energy equals half the mass times the velocity squared. Rearranged, m = 2KE / v² and v = √(2KE / m). The calculator solves for whichever value you leave blank and shows the answer in joules.
- SI units: joules (J) for energy, kilograms (kg) for mass, metres per second (m/s) for velocity. You may enter other units (kJ, cal, g, lb, km/h, mph); the tool converts to SI and shows the result in SI with a dimmed US/imperial readout below.
- Because velocity is squared in the formula. If the velocity doubles, v² becomes four times as large, so the kinetic energy is also four times as large. This is why speed limits matter so much for road safety.
- Yes. Enter two of kinetic energy, mass and velocity and leave the third blank — the calculator rearranges KE = ½mv² and solves for the missing value, including taking a square root when solving for velocity.
- No. Because mass is always positive and velocity is squared, kinetic energy is always zero or positive. It is zero only when the object is not moving.
- The physics — KE = ½mv² in SI units — is identical worldwide. What changes is the terminology; "kinetic energy" is 动能 in Chinese, while SPM students see the Malay term. The calculated value is the same.
- The Tool Information block lists the exact syllabus for your selected curriculum (e.g. SPM Fizik 4531). It is a study aid, not a substitute for your official syllabus or teacher.
- No. Every calculation runs in your browser; nothing you type is uploaded. It works offline once the page has loaded.
- Completely free, no account or usage limit. It runs entirely in your browser and collects no data.
Method & sources
How it computes
KE = 1/2 m v^2, which is the LOW-SPEED LIMIT of the relativistic expression (gamma - 1) m c^2. At 10% of light speed the classical value is already about 0.4% low; at 50% it is out by 19%. For anything terrestrial the difference is irrelevant, and the tool says which regime it is in rather than leaving it implied.
What this tool implements
- Classical, and labelled as such. The relativistic correction is stated so a result at high velocity is not read as exact.
- The joule is the SI derived unit kg m^2 s^-2; inputs are taken in SI rather than assuming a unit system.
- Kinetic energy is frame-dependent. It has no absolute value — a different inertial observer computes a different number for the same object, correctly.
Sources
- BIPM, The International System of Units (SI Brochure), 9th edition 2019 — the joule: https://www.bipm.org/en/publications/si-brochure
- Einstein A. Zur Elektrodynamik bewegter Korper. Annalen der Physik 1905;322(10):891-921 — the relativistic energy relation this approximates: https://doi.org/10.1002/andp.19053221004
What can make this go out of date
- None.
Pick up where you left off
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