Energy Converter
Convert energy and work between joules, calories, kilowatt-hours, Btu, electronvolts and many other units. Pick two units, type a value and read the result.
Select two units to see the conversion factor.
This tool converts energy. kW and kWh are different: kW is power, kWh is energy. Torque units (N·m, lbf·ft) are not energy and are in the Torque Converter.
Energy Formula
Every energy unit is a fixed multiple of the joule. Result = value × (size of source unit in J ÷ size of target unit in J). Exact sizes: 1 Wh = 3,600 J, 1 kWh = 3,600,000 J, 1 cal (IT) = 4.1868 J, 1 cal (thermochemical) = 4.184 J, 1 Btu (IT) = 1,055.05585262 J and 1 eV = 1.602176634 × 10⁻¹⁹ J.
What Is Energy?
Energy is the ability to do work or produce heat. The SI unit is the joule (J). Lifting a small apple one meter takes about one joule.
The list has several groups. SI and electrical: joule with prefixes, watt-second, watt-hour, kilowatt-hour, megawatt-hour and gigawatt-hour. Heat units: calorie, kilocalorie, Btu, therm and ton-hour of refrigeration. Mechanical work: foot-pound, inch-pound, kilogram-force meter and horsepower-hour. Small-scale and CGS: erg, dyne centimeter, electronvolt, Hartree and Rydberg energy. Explosive energy: ton, kiloton, megaton and gigaton of TNT.
Which calorie? There is more than one calorie. The International Table calorie (IT) is exactly 4.1868 J. The thermochemical calorie (th) is exactly 4.184 J. They differ by about 0.07%. The food Calorie (capital C) equals one kilocalorie. This tool uses the IT kilocalorie for it. Some food labels use 4.184 kJ per kcal, so pick “kcal (th)” if you want that value.
Energy is not power. A kilowatt (kW) is a rate of using energy. A kilowatt-hour (kWh) is an amount of energy: a 1 kW heater running for one hour uses 1 kWh. Power units such as watts and horsepower are not offered here.
Energy is not torque. A newton meter can mean torque (a twist) or energy (a joule). Torque and energy are different things, so torque-named units are kept out of this tool. Foot-pound and inch-pound are shown as work units (force × distance moved).
Supported Units
This converter supports the following 46 energy units. The last column gives the size of each unit in joules.
| Unit | Symbol | Value in J |
|---|---|---|
| Joule | J | 1 |
| Gigajoule | GJ | 1,000,000,000 |
| Megajoule | MJ | 1,000,000 |
| Kilojoule | kJ | 1,000 |
| Millijoule | mJ | 0.001 |
| Microjoule | µJ | 1e-6 |
| Nanojoule | nJ | 1e-9 |
| Attojoule | aJ | 1e-18 |
| Watt-hour | W·h | 3,600 |
| Kilowatt-hour | kW·h | 3,600,000 |
| Megawatt-hour | MW·h | 3,600,000,000 |
| Gigawatt-hour | GW·h | 3.6e+12 |
| Watt-second | W·s | 1 |
| Kilowatt-second | kW·s | 1,000 |
| Calorie (IT) | cal (IT) | 4.1868 |
| Calorie (thermochemical) | cal (th) | 4.184 |
| Kilocalorie (IT) | kcal (IT) | 4,186.8 |
| Kilocalorie (thermochemical) | kcal (th) | 4,184 |
| Calorie (nutritional, Cal = 1 kcal IT) | Cal | 4,186.8 |
| British thermal unit (IT) | Btu (IT) | 1,055.055853 |
| British thermal unit (thermochemical) | Btu (th) | 1,054.35 |
| Mega Btu (IT) | MBtu (IT) | 1,055,055,853 |
| Therm (EC, 100 000 Btu IT) | therm (EC) | 105,505,585.3 |
| Therm (US) | therm (US) | 105,480,400 |
| Horsepower-hour (mechanical) | hp·h | 2,684,519.538 |
| Horsepower-hour (metric) | PS·h | 2,647,795.5 |
| Ton-hour (refrigeration) | TR·h | 12,660,670.23 |
| Erg | erg | 1e-7 |
| Dyne centimeter | dyn·cm | 1e-7 |
| Electronvolt | eV | 1.602176634e-19 |
| Kiloelectronvolt | keV | 1.602176634e-16 |
| Megaelectronvolt | MeV | 1.602176634e-13 |
| Ton of TNT (explosives) | ton TNT | 4,184,000,000 |
| Kiloton of TNT | kton | 4.184e+12 |
| Megaton of TNT | Mton | 4.184e+15 |
| Gigaton of TNT | Gton | 4.184e+18 |
| Foot-pound (force) | ft·lbf | 1.355817948 |
| Inch-pound (force) | in·lbf | 0.112984829 |
| Inch-ounce (force) | in·ozf | 0.007061551814 |
| Poundal foot | pdl·ft | 0.04214011009 |
| Gram-force centimeter | gf·cm | 9.80665e-5 |
| Gram-force meter | gf·m | 0.00980665 |
| Kilogram-force centimeter | kgf·cm | 0.0980665 |
| Kilogram-force meter (kilopond meter) | kgf·m | 9.80665 |
| Hartree energy | Eh | 4.359744722e-18 |
| Rydberg energy | Ry | 2.179872361e-18 |
How to Use the Energy Converter
- Type the energy in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (J): 1 kcal (IT) = 4,186.8 J and 1 kJ = 1,000 J.
- Divide the source size by the target size to get the conversion factor: 4,186.8 ÷ 1,000 = 4.1868, so 1 kcal (IT) = 4.1868 kJ.
- Multiply by your value: 250 kcal (IT) × 4.1868 = 1,046.7 kJ.
Energy cannot be negative here, so enter zero or a positive number.
Common Energy Conversions
- Food: 250 kcal equals 1,046.7 kJ, and 1,000 kJ equals 238.8458966 kcal.
- Electricity bill: 1 kWh equals 3.6 MJ and 3,412.141633 Btu.
- Phone battery: 15 Wh equals 54 kJ.
- Heating: 10,000 Btu equals 10.55055853 MJ and 2.930710702 kWh.
- Gas bills: 1 therm (US) equals 29.30011111 kWh.
- Mechanical work: 100 ft·lbf equals 135.5817948 J.
- Physics: 1 eV equals 1.602176634e-19 J.
- Explosives: 1 kiloton of TNT equals 4,184 GJ.
Kilocalorie (IT) to Other Energy Units
Quick reference for frequently used values
| kcal | kJ | Wh | Btu |
|---|---|---|---|
| 1 | 4.1868 | 1.163 | 3.968320719 |
| 10 | 41.868 | 11.63 | 39.68320719 |
| 50 | 209.34 | 58.15 | 198.416036 |
| 100 | 418.68 | 116.3 | 396.8320719 |
| 250 | 1,046.7 | 290.75 | 992.0801798 |
| 500 | 2,093.4 | 581.5 | 1,984.16036 |
| 1,000 | 4,186.8 | 1,163 | 3,968.320719 |
| 2,000 | 8,373.6 | 2,326 | 7,936.641439 |
Where and Why This Conversion Is Used
- Nutrition: kilocalories and kilojoules on food labels.
- Electricity: kWh on bills, Wh on batteries.
- Heating and cooling: Btu, therm and refrigeration ton-hours.
- Fuel and gas: megajoules, therms and kWh on gas bills.
- Physics and chemistry: eV, erg, Hartree.
- Safety and defense studies: TNT equivalents.
Important Limitations
- The tool does not convert power (W, kW, hp) to energy. You must multiply power by time first.
- It does not convert torque to energy. Torque units are in the Torque Converter.
- Different calories and Btu exist. Check which one your source uses (IT or thermochemical).
- Fuel-oil “equivalents” and similar trade figures are left out, because their definitions vary by country and year.