Updated on September 5th, 2025

E = mc² Calculator

Created By Jehan Wadia

E = mc2
Quick Examples:

About E = mc²: Einstein's mass-energy equivalence equation shows that mass and energy are interchangeable. The speed of light squared (c²) is approximately 9 × 10¹⁶ m²/s², meaning even tiny amounts of mass contain enormous energy.

Introduction

The E = mc² calculator helps you explore Einstein's famous equation that shows how mass and energy are connected. This simple formula reveals that even tiny amounts of matter contain huge amounts of energy. When you multiply mass (m) by the speed of light squared (c²), you get the total energy (E) stored in that mass.

Use this tool to calculate energy from mass, find out how much mass equals a certain amount of energy, or even solve for the speed of light. You can work with many different units - from tiny electron masses to kilograms, and from electron volts to megatons of TNT. The calculator shows real-world comparisons to help you understand these huge energy values, like how many lightning bolts or days of home power your result equals.

How to use our E = mc² Calculator

Enter mass and speed values to find energy, or pick what you want to solve for. The calculator will show you the result using Einstein's famous equation.

Solve For: Pick whether you want to find energy, mass, or speed of light from the dropdown menu.

Mass (m): Type in the mass value and pick your unit like kilograms, grams, or pounds.

Energy (E): Type in the energy value and pick your unit like Joules, kilowatt-hours, or electron volts.

Speed of Light (c): This value stays at 299,792,458 meters per second unless you change the unit.

Decimal Precision: Choose how many decimal places you want to see in your answer.

Notation: Pick between standard numbers or scientific notation for very big or small numbers.

Quick Examples: Click any preset button to load sample values for electrons, protons, or other common examples.

Understanding E = mc²: Einstein's Famous Equation

E = mc² is one of the most famous equations in physics. It was created by Albert Einstein in 1905. This simple equation shows that mass and energy are really two forms of the same thing. The letter E stands for energy, m stands for mass, and c is the speed of light. The small 2 means the speed of light is squared (multiplied by itself).

What Makes This Equation Special

The speed of light is a huge number - about 300,000 kilometers per second. When you square this number, it becomes even bigger. This means that even a tiny amount of mass contains an enormous amount of energy. For example, if you could convert just one gram of matter completely into energy, it would release as much energy as burning thousands of tons of coal. You can explore similar energy concepts with our Kinetic Energy Calculator or Potential Energy Calculator.

How Mass Becomes Energy

In the real world, mass can be converted to energy in several ways. The sun creates energy by turning a small amount of hydrogen mass into energy through fusion. Nuclear power plants use this same idea but with uranium atoms. Even in regular chemical reactions like burning wood, a tiny bit of mass is converted to energy, though the amount is so small we can't measure it easily. To understand how forces relate to energy, try our Force Calculator or explore gravitational effects with the Gravitational Force Calculator.

Why This Matters

This equation helps us understand how the sun shines, how nuclear power works, and even how the universe was created. It shows that matter and energy are connected in a deep way. This discovery changed how we think about the universe and led to many important technologies we use today, from medical scans to smoke detectors to GPS satellites that need to account for these effects to work properly. For motion-related calculations that also depend on fundamental physics principles, check out our Free Fall Calculator.


Frequently Asked Questions

What does each letter in E = mc² mean?

In the equation E = mc²:

Why does the calculator show such huge energy numbers?

The speed of light is very fast - about 300,000 kilometers per second. When you square this huge number (multiply it by itself), it becomes even bigger - about 90,000,000,000,000,000! This means even a tiny bit of mass contains enormous energy. For example, one gram of matter has as much energy as 20,000 tons of TNT.

Can I really convert mass into energy?

Yes, but only in special ways. The sun does this through nuclear fusion. Nuclear power plants do it through nuclear fission. Even burning wood converts a tiny bit of mass to energy, but the amount is too small to notice. You cannot convert everyday objects completely into energy at home - this only happens in stars, nuclear reactors, or particle accelerators.

What are the preset buttons for?

The preset buttons load real examples to help you learn. Click 'Electron' to see the energy in one electron. Click 'Proton' for a proton's energy. Click '1 gram of matter' to see how much energy is in a paperclip. These examples help you understand the huge amounts of energy in tiny masses.

What units should I use for my calculation?

Use any units that make sense for your problem. For everyday objects, use grams or kilograms for mass. For atomic particles, use atomic mass units (amu). For energy, Joules work well for science problems, while kilowatt-hours help you understand home energy use. The calculator converts between all units automatically.

What do the energy comparisons mean?

The comparisons help you understand the huge energy values. The calculator might show your result equals several lightning bolts, days of home power, or fractions of atomic bombs. These real-world examples make it easier to grasp how much energy you're talking about, since the raw numbers can be hard to imagine.

Can I solve for the speed of light?

Yes! Change 'Solve For' to 'Speed of Light' and enter mass and energy values. This shows you what the speed of light would need to be for your values to work. This helps you understand why the speed of light must be so fast - slower speeds wouldn't create enough energy from mass.

What's the difference between standard and scientific notation?

Standard notation shows regular numbers like 1,000,000. Scientific notation shows the same number as 1×10⁶. Scientific notation is better for very big or very small numbers because it's easier to read. The calculator picks the best format automatically unless you choose one.