This energy unit converter changes a quantity of energy between 13 units, including joules, kilowatt-hours, calories, kilocalories and British thermal units. Every value goes through the joule, the SI unit. Two key factors are exact: 1 kWh = 3,600,000 J and 1 thermochemical calorie = 4.184 J. One international-table BTU is about 1,055.06 J.
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How to use the energy unit converter
- In the energy unit converter, enter the amount, such as 900 from an electricity bill.
- Pick its unit (kWh) and the unit you want (for example MJ or BTU).
- Read the result; the energy unit converter keeps full precision until it is displayed.
Food labels in the US print “Calories” with a capital C. That is a kilocalorie, 4,184 J. Pick kcal, not cal, when converting food energy, or the result will be 1,000 times too small.
What is energy?
Energy is the capacity to do work. The SI unit is the joule (J). Food energy is given in kilocalories (1 kcal = 4.184 kJ), electricity in kilowatt-hours (1 kWh = 3.6 MJ) and heating fuel in BTUs or therms.
Conversion formula
The energy unit converter stores every unit as a multiple of the base unit, the joule (J). To convert:
value in target unit = value × (factor of source unit ÷ factor of target unit)
where each factor is the size of the unit in joules.
Common energy conversions
| From | To | 1 unit equals |
|---|---|---|
| joule (J) | calorie (cal) | 0.2390057 cal |
| calorie (cal) | joule (J) | 4.184 J |
| kilowatt hour (kWh) | megajoule (MJ) | 3.6 MJ |
| kilocalorie (kcal) | kilojoule (kJ) | 4.184 kJ |
| British thermal unit (BTU) | joule (J) | 1,055.056 J |
| joule (J) | British thermal unit (BTU) | 0.0009478171 BTU |
| watt hour (Wh) | joule (J) | 3,600 J |
| foot-pound (ft·lb) | joule (J) | 1.355818 J |
| therm (thm US) | megajoule (MJ) | 105.4804 MJ |
| kilojoule (kJ) | kilocalorie (kcal) | 0.2390057 kcal |
Energy unit converter worked example
Convert 25 kilowatt hours to megajoules:
- Factor of kWh = 3,600,000 J
- Factor of MJ = 1,000,000 J
- 25 × 3,600,000 ÷ 1,000,000 = 90 MJ
Energy unit reference
| Unit | Symbol | Group | Equals (J) |
|---|---|---|---|
| Joule | J | SI | 1 |
| Kilojoule | kJ | SI | 1,000 |
| Megajoule | MJ | SI | 1,000,000 |
| Calorie (thermochemical) | cal | Common | 4.184 |
| Kilocalorie (thermochemical) | kcal | Common | 4,184 |
| Watt Hour | Wh | Electrical | 3,600 |
| Kilowatt Hour | kWh | Electrical | 3,600,000 |
| Megawatt Hour | MWh | Electrical | 3,600,000,000 |
| British Thermal Unit (IT) | BTU | US/Imperial | 1,055.055853 |
| Electronvolt | eV | Physics | 1.60218 × 10−19 |
| Erg | erg | CGS | 1 × 10−7 |
| Therm (US) | thm US | US | 105,480,400 |
| Foot-pound | ft·lb | US/Imperial | 1.355817948 |
| Kilowatt Second | kWs | Electrical | 1,000 |
| Gigajoule | GJ | SI | 1,000,000,000 |
Reverse factors for each energy unit
The energy unit converter reference table gives each unit in joules. To go the other way, divide by that factor; the list below does the division for you.
- Kilojoule (kJ), SI: 1 kJ = 1,000 J, so 1 J = 0.001 kJ.
- Megajoule (MJ), SI: 1 MJ = 1,000,000 J, so 1 J = 1 × 10−6 MJ.
- Calorie (thermochemical) (cal), Common: 1 cal = 4.184 J, so 1 J = 0.2390057 cal.
- Kilocalorie (thermochemical) (kcal), Common: 1 kcal = 4,184 J, so 1 J = 0.0002390057 kcal.
- Watt Hour (Wh), Electrical: 1 Wh = 3,600 J, so 1 J = 0.0002777778 Wh.
- Kilowatt Hour (kWh), Electrical: 1 kWh = 3,600,000 J, so 1 J = 2.77778 × 10−7 kWh.
- Megawatt Hour (MWh), Electrical: 1 MWh = 3.6 × 109 J, so 1 J = 2.77778 × 10−10 MWh.
- British Thermal Unit (IT) (BTU), US/Imperial: 1 BTU = 1,055.056 J, so 1 J = 0.0009478171 BTU.
- Electronvolt (eV), Physics: 1 eV = 1.60218 × 10−19 J, so 1 J = 6.2415 × 1018 eV.
- Erg (erg), CGS: 1 erg = 1 × 10−7 J, so 1 J = 1 × 107 erg.
- Therm (US) (thm US), US: 1 thm US = 1.0548 × 108 J, so 1 J = 9.48043 × 10−9 thm US.
- Foot-pound (ft·lb), US/Imperial: 1 ft·lb = 1.355818 J, so 1 J = 0.7375621 ft·lb.
- Kilowatt Second (kWs), Electrical: 1 kWs = 1,000 J, so 1 J = 0.001 kWs.
- Gigajoule (GJ), SI: 1 GJ = 1 × 109 J, so 1 J = 1 × 10−9 GJ.
kWh to joules, calories to joules and BTU to kWh
Three conversions cover most everyday questions:
- kWh to joules: multiply by 3,600,000. A 60 kWh car battery holds 216 MJ.
- Calories to joules: multiply by 4.184, or by 4,184 for food Calories. A 300-Calorie snack is about 1.26 MJ.
- BTU to kWh: divide by about 3,412.14. A furnace rated at 30,000 BTU per hour delivers about 8.79 kWh of heat in one hour.
The energy unit conversion table in the image above lists the same factors for seven common amounts.
Everyday energy amounts in joules and kWh
Putting familiar quantities in one unit makes them comparable. The household figure is the US Energy Information Administration average for 2022 (10,791 kWh a year); the gasoline value is EIA’s 2026 estimate of heat content per gallon:
| Item | Typical value | Joules | kWh |
|---|---|---|---|
| US monthly home electricity use (EIA average) | about 899 kWh | 3.24 GJ | 899 |
| Daily food intake | 2,000 kcal | 8.368 MJ | 2.324 |
| One therm of natural gas | 100,000 BTU | 105.5 MJ | 29.31 |
| Gallon of gasoline (EIA) | about 120,166 BTU | 126.8 MJ | 35.2 |
A day of food energy is only about 2.3 kWh, which is why a person at rest averages roughly 100 W.
Energy vs power: kWh and kW
Energy is an amount; power is a rate. A kilowatt (kW) is 1,000 joules per second, and a kilowatt-hour is the energy used by a 1 kW load running for one hour. A 1,500 W space heater on for 4 hours uses 6 kWh, or 21.6 MJ. For rates such as watts or BTU per hour, use the power unit converter.
Related converters and calculators
For bills, heating and food energy, these tools go further than the energy unit converter:
- Electricity calculator: cost of running an appliance
- BTU calculator: heating and cooling size
- Calorie calculator: daily energy needs
- Calories burned calculator: exercise energy
- Power unit converter: W, kW, hp and BTU/h
Sources
The energy unit converter is based on these sources: NIST Special Publication 811, Appendix B; US EIA: Units and calculators explained; US EIA: average household electricity use.
Questions about this calculator
What is the SI unit of energy?
The joule (J), equal to one newton-meter or one watt-second. Every unit in this energy unit converter is defined as a multiple of the joule.
How do I convert kWh to joules?
Multiply by 3,600,000. One kilowatt-hour is exactly 3.6 MJ, so 2.5 kWh = 9,000,000 J.
How do I convert calories to joules?
Multiply calories by 4.184. For food Calories (kilocalories) multiply by 4,184: 250 kcal = 1,046,000 J, or about 1.05 MJ.
How do I convert BTU to kWh?
Divide BTU by about 3,412.14. For example, 10,000 BTU = 2.93 kWh.
How many kWh is a therm?
One therm is 100,000 BTU, about 29.31 kWh or 105.5 MJ.
Is a food Calorie the same as a calorie?
No. A food Calorie is a kilocalorie, 1,000 small calories or 4,184 J.
Why are there different BTU and calorie values?
Older definitions were based on heating water at particular temperatures. This converter uses the international-table BTU and the thermochemical calorie listed in NIST SP 811.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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