# E = mc² Calculator

URL: https://speedycalculator.com/calculators/physics/mass-energy/
Last updated: 2026-10-25

> The E = mc² calculator converts mass into its equivalent energy using Einstein’s equation, in joules, kilowatt-hours and tons of TNT.

## Inputs

- Mass (g, kg, mg)

## Results

- Energy
- In kilowatt-hours
- TNT equivalent

## Formula

```
E = m c²
```

## Explanation

A tiny amount of mass corresponds to an enormous amount of energy because the speed of light squared is huge.

### How to use the E = mc² Calculator

- **Mass**
- Want to work backwards? Type a value into **Energy** and **Mass** is calculated for you.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Multiply mass in kilograms by the speed of light squared.

### What each result means

- **Energy** = [Mass] × 299792458^2
- **In kilowatt-hours** = [Energy] ÷ 3.6e6
- **TNT equivalent** = [Energy] ÷ 4.184e12

### Example values

How the main result changes when **Mass** changes and everything else stays at the example values above:

Mass (g)Energy (J)0.544,937,758,936,840.880.7567,406,638,405,261.32189,875,517,873,681.771.25112,344,397,342,102.21.5134,813,276,810,522.642179,751,035,747,363.53

## Worked example

Inputs — Mass: 1 g.

Results — **Energy = 89,875,517,873,681.77 J**; In kilowatt-hours = 24,965,422 kWh; TNT equivalent = 21.481 kilotons.

## FAQ

**How much energy is in one gram?**
About 9 × 10¹³ J, around 21 kilotons of TNT.

**Does a nuclear reactor convert all its fuel to energy?**
No, only a tiny fraction of the mass is converted.

**What formula does the E = mc² Calculator use?**
E = m c².

**Can I work backwards from the result?**
Yes. Type the result you want into Energy and the calculator finds the matching mass.


## Sources

- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)