An energy converter for electricity, food, fuel and physics
Energy turns up as kilowatt-hours on an electricity bill, kilocalories on a food label, BTU on a heater, therms on a gas bill and electronvolts in a physics textbook. This energy converter links them all through the joule, the SI unit, and shows your value in fourteen units at once with the exact factor used.
Use it to compare a gas tariff in therms with an electricity tariff per kWh, to see how many kilojoules are in a 250 kcal snack, to estimate how much energy a day’s food really is, or to check homework that mixes joules, calories and electronvolts.
How to use the Energy Converter
- Enter an amount of energy in the Value box, such as 2000 or 3.5.
- Select its unit under From — search “kWh”, “kcal”, “BTU” or “therm”.
- Select the unit you want under To; the round swap button reverses the pair.
- Read the answer and the formula. Change Precision for more or fewer digits and press Copy.
- Scan the list of every energy unit beneath, or tap a common conversion like “1 kWh → MJ”.
Energy Converter features
Electricity units
Wh, kWh and MWh — the kWh is the “unit” printed on household electricity bills in India and the UK.
Food energy done right
The kilocalorie on nutrition labels (the capital-C Calorie) is kept distinct from the small calorie, so a 2,000 kcal diet is never mistaken for 2,000 cal.
Heating and fuel units
International Table BTU and the therm of 100,000 BTU for boilers, furnaces and gas bills.
Physics and mechanics
Electronvolts, ergs and foot-pounds force alongside joules, kJ, MJ and GJ.
Exact modern definitions
Factors follow the current SI, including the electronvolt fixed exactly in 2019.
Energy conversion factors
One joule is the work done by a force of one newton over one metre, or one watt for one second. Electricity units follow directly: a watt-hour is 3,600 J and a kilowatt-hour is 3.6 MJ. The calorie began as the heat needed to warm a gram of water by one degree Celsius; the version used in chemistry and nutrition is the thermochemical calorie of exactly 4.184 J.
| Unit | Value in joules | Where you see it |
|---|---|---|
| Kilojoule (kJ) | 1,000 | Food labels in Australia and the EU |
| Watt-hour (Wh) | 3,600 | Batteries, power banks |
| Kilowatt-hour (kWh) | 3,600,000 | Electricity bills, EV batteries |
| Calorie (cal) | 4.184 | Chemistry |
| Kilocalorie (kcal, food Calorie) | 4,184 | Nutrition labels, diets |
| British thermal unit (BTU) | 1,055.05585262 | Heating and cooling in the US |
| Therm (100,000 BTU) | 105,505,585.262 | Gas bills in the UK and US |
| Foot-pound force (ft·lbf) | ≈ 1.3558179 | Mechanical work, firearms |
| Erg | 0.0000001 | CGS physics |
| Electronvolt (eV) | 1.602176634 × 10⁻¹⁹ (exact) | Atomic and particle physics |
Worked examples
kWh to MJ — multiply by 3.6. A 2 kW heater running for 3 hours uses 6 kWh, which is 21.6 MJ. The electricity bill calculator turns kWh into money.
kcal to kJ — multiply by 4.184. A 250 kcal chocolate bar contains 1,046 kJ. A 2,000 kcal day of food is 8.368 MJ, or about 2.32 kWh — roughly what a 100 W bulb uses if left on for a whole day. For personal energy needs, try the calorie calculator.
Therms to kWh — multiply by about 29.307. A month using 50 therms of gas is about 1,465 kWh, which lets you compare it with an electric heating quote.
kWh to BTU — multiply by about 3,412.14. This is the bridge between electric and gas appliance ratings in the US.
Energy vs power: kWh is not kW
Power is the rate of using energy; energy is the total used. A kilowatt (kW) is a rate, and a kilowatt-hour (kWh) is an amount: one kilowatt sustained for one hour. A 1.5 kW kettle that runs for 4 minutes uses 1.5 × 4/60 = 0.1 kWh. If you are converting watts, horsepower or BTU per hour, use the power converter instead.
Common energy conversions
| From | To |
|---|---|
| 1 kWh | 3.6 MJ |
| 1 MJ | 0.2777777778 kWh |
| 1 kWh | 3,412.141633 BTU |
| 1 kWh | 860.4206501 kcal |
| 1 kcal | 4.184 kJ |
| 1,000 kJ | 239.0057361 kcal |
| 1 cal | 4.184 J |
| 1 BTU | 1,055.055853 J |
| 1 BTU | 0.2521644007 kcal |
| 1 thm | 29.30710702 kWh |
| 1 ft·lbf | 1.355817948 J |
| 1 eV | 1.602176634 × 10⁻¹⁹ J |
Tips and common mistakes
- Calorie or Calorie? Food “Calories” are kilocalories. A label showing 200 Calories means 200 kcal = 836.8 kJ, not 200 small calories.
- Two calories exist. Besides the thermochemical calorie (4.184 J) used here, engineering steam tables use the International Table calorie of 4.1868 J — a 0.07% difference.
- Two therms exist. This converter uses the therm of 100,000 International Table BTU (105.506 MJ); the US therm is slightly smaller at 105.4804 MJ.
Energy Converter FAQ
How many joules are in a kWh?
Exactly 3,600,000 joules (3.6 MJ), because one kilowatt is 1,000 joules per second and an hour has 3,600 seconds.
How do I convert kcal to kJ?
Multiply by 4.184. For example, 500 kcal × 4.184 = 2,092 kJ. To go from kJ to kcal, divide by 4.184.
Is a food Calorie the same as a kilocalorie?
Yes. The Calorie with a capital C on food labels equals one kilocalorie, or 4,184 joules. The energy converter labels it “Kilocalorie (food Calorie)”.
How many BTU are in a kWh?
One kilowatt-hour is about 3,412.14 BTU, and one BTU is about 0.000293 kWh (1,055.06 J).
What is a therm in kWh?
One therm (100,000 BTU) is about 29.31 kWh. UK gas bills now show usage in kWh, calculated from the volume of gas and its calorific value.
What is an electronvolt?
The energy an electron gains when accelerated through one volt: exactly 1.602176634 × 10⁻¹⁹ J. It is used for atomic, X-ray and particle energies.