Quick answer
Energy units convert through joules. 1 megawatt-hour equals 1,000 kilowatt-hours, and 1 kWh equals 3.6 million joules.
Enter a value and choose the units. The calculator returns the converted energy.
Related tools: Potential Energy Calculator: Gravitational potential energy from mass, height and gravity. Kinetic Energy Calculator: Kinetic energy and momentum of a moving mass. Photon Energy Calculator: Photon energy from wavelength or frequency.
How to use the Energy Converter
- Enter value.
- Choose from: Joule (J), Kilojoule (kJ), Megajoule (MJ), Gigajoule (GJ), Calorie (cal, thermochemical) and Kilocalorie (kcal) and 13 more.
- Choose to: Joule (J), Kilojoule (kJ), Megajoule (MJ), Gigajoule (GJ), Calorie (cal, thermochemical) and Kilocalorie (kcal) and 13 more.
- Enter decimal places (between 0 and 10). It starts at 4.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Value | A number | — |
| From | Choose one: Joule (J); Kilojoule (kJ); Megajoule (MJ); Gigajoule (GJ); Calorie (cal, thermochemical); Kilocalorie (kcal); Watt-hour (Wh); Kilowatt-hour (kWh); … | Starts at Joule (J) |
| To | Choose one: Joule (J); Kilojoule (kJ); Megajoule (MJ); Gigajoule (GJ); Calorie (cal, thermochemical); Kilocalorie (kcal); Watt-hour (Wh); Kilowatt-hour (kWh); … | Starts at Kilojoule (kJ) |
| Decimal places | A number | ≥ 0, ≤ 10, starts at 4 |
Formula and method
Formula
result = value × (factor of source ÷ factor of target), base unit: joule
IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Every unit is defined by an exact or published factor to the base unit (joule). The value is multiplied by the source factor and divided by the target factor.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Value = 1; From = Megawatt-hour (MWh); To = Kilowatt-hour (kWh); Decimal places = 4.
| Result | Value |
|---|---|
| Megawatt-hour (MWh) → Kilowatt-hour (kWh) | 1,000 |
| Input | 1 Megawatt-hour (MWh) |
Example 2
Inputs: Value = 1; From = Million BTU (MMBtu); To = BTU (International Table); Decimal places = 0.
| Result | Value |
|---|---|
| Million BTU (MMBtu) → BTU (International Table) | 1,000,000 |
| Input | 1 Million BTU (MMBtu) |
Example 3
Inputs: Value = 1; From = Kilowatt-hour (kWh); To = Megajoule (MJ); Decimal places = 4.
| Result | Value |
|---|---|
| Kilowatt-hour (kWh) → Megajoule (MJ) | 3.6 |
| Input | 1 Kilowatt-hour (kWh) |
The first line is the headline result (megawatt-hour (MWh) → Kilowatt-hour (kWh)). Below it the energy Converter lists input, which describe the same case from other angles. IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Unit reference
Each unit expressed in the base unit used for the calculation. Conversions go through this base unit, so any unit can be converted to any other in the table.
| Unit | Equals (in joule) |
|---|---|
| Joule (J) | 1 |
| Kilojoule (kJ) | 1000 |
| Megajoule (MJ) | 1000000 |
| Gigajoule (GJ) | 1000000000 |
| Calorie (cal, thermochemical) | 4.184 |
| Kilocalorie (kcal) | 4184 |
| Watt-hour (Wh) | 3600 |
| Kilowatt-hour (kWh) | 3600000 |
| Megawatt-hour (MWh) | 3600000000 |
| Gigawatt-hour (GWh) | 3600000000000 |
| Million BTU (MMBtu) | 1055055853 |
| BTU (International Table) | 1055.055853 |
| Electronvolt (eV) | 1.602176634e-19 |
| Foot-pound force (ft·lbf) | 1.355817948 |
| Watt-second (W·s) | 1 |
| Megacalorie (Mcal) | 4184000 |
| Megaelectronvolt (MeV) | 1.602176634e-13 |
| Therm (US) | 105480400 |
| Quad (10¹⁵ BTU) | 1055055853000000000 |
Common values
1 kWh = 3,600 kJ = 3.6 MJ = 860 kcal = 3,412 BTU. 1 kcal (food calorie) = 4,184 J. 1 BTU = 1,055 J. Electricity bills use kWh; gas bills may use therms or cubic feet.
Energy versus power
Energy is power multiplied by time. A 1 kW heater running for an hour uses 1 kWh. Do not mix kW (power) with kWh (energy) when comparing devices.
How the result changes with value
Holding every other input at the first worked example, this table changes only value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Value | Megawatt-hour (MWh) → Kilowatt-hour (kWh) | Input |
|---|---|---|
| 0.5 | 500 | 0.5 Megawatt-hour (MWh) |
| 1 | 1,000 | 1 Megawatt-hour (MWh) |
| 2 | 2,000 | 2 Megawatt-hour (MWh) |
| 4 | 4,000 | 4 Megawatt-hour (MWh) |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: left empty shows "Enter value." beside that field and no result.
Choosing between the Energy Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Potential Energy Calculator](/science/potential-energy-calculator/) | mass, height and gravitational acceleration | Potential energy |
| [Kinetic Energy Calculator](/science/kinetic-energy-calculator/) | mass and speed | Kinetic energy |
| [Photon Energy Calculator](/science/photon-energy-calculator/) | start from and wavelength or frequency | Photon energy |
| [Power Calculator](/science/power-calculator/) | use | Power |
| [Solar Panel Output Calculator](/science/solar-panel-output-calculator/) | panel rating, number of panels and peak sun hours per day | Energy |
Background: unit conversion
Many customary units are defined exactly in terms of metric ones: since the 1959 International Yard and Pound Agreement an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg (NIST SP 811 lists these). So most length and mass conversions are exact apart from the rounding of the displayed result.
To convert, multiply the value by the source unit's factor to reach the base unit, then divide by the target unit's factor; the unit table on this page lists every factor used. Temperature and fuel economy are the exceptions, because they are not simple multiples.
Assumptions and limitations
- Negative values are allowed
- Zero converts to zero (except L/100 km, where zero is invalid)
- Units from different quantities cannot be converted
- Very large or tiny results switch to exponent notation
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value to confirm this.
Frequently asked questions
How many joules in a calorie?
A small calorie is 4.184 J; a food Calorie is 4,184 J.
How many kWh in a MWh?
One megawatt-hour is 1,000 kilowatt-hours.
What is a BTU?
The heat to raise one pound of water by one degree Fahrenheit, about 1,055 J.
What does the Energy Converter calculate?
Convert joules, calories, kWh, BTU and more. It returns Megawatt-hour (MWh) → Kilowatt-hour (kWh) and Input.
What formula does the Energy Converter use?
result = value × (factor of source ÷ factor of target), base unit: joule. Every unit is defined by an exact or published factor to the base unit (joule).
What is an example of a energy result?
With value 1, from Megawatt-hour (MWh), to Kilowatt-hour (kWh) and decimal places 4, the megawatt-hour (MWh) → Kilowatt-hour (kWh) is 1,000.
Where does the method come from?
The method follows: NIST SP 811 (2008): thermochemical calorie = 4.184 J exactly; International Table BTU = 1055.05585262 J; CODATA 2018: eV = 1.602176634e-19 J exactly.
Related calculators
- Potential Energy Calculator — Gravitational potential energy from mass, height and gravity.
- Kinetic Energy Calculator — Kinetic energy and momentum of a moving mass.
- Photon Energy Calculator — Photon energy from wavelength or frequency.
- Power Calculator — Mechanical power from work and time, or force and velocity.
- Solar Panel Output Calculator — Daily, monthly and yearly energy from a solar array.
- Solar Payback Calculator — Simple payback period of an installation after incentives.
Sources
- NIST SP 811 (2008): thermochemical calorie = 4.184 J exactly
- International Table BTU = 1055.05585262 J
- CODATA 2018: eV = 1.602176634e-19 J exactly
- NIST SP 811 (2008): therm (U.S.) = 1.054804e8 J; quad = 10^15 BTU (International Table)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.