How to use this energy converter
- Type the amount of energy in the From box. The page opens with 2,000.
- Pick its unit in the From menu. For food, choose "Kilocalorie, food Calorie (kcal)". The list also has joules, kilojoules, megajoules, watt-hours, kilowatt-hours, megawatt-hours, BTU, therms, foot-pounds and electronvolts.
- Pick the unit you want in the To menu. The To box updates as you type, and typing in the To box converts the other way.
- Press Swap units to flip the menus. The panel below lists the same energy in every unit.
How the conversion works
Every amount is converted to joules and then to your target unit: value × (From unit in J) ÷ (To unit in J). A watt-hour is 3,600 J and a kilowatt-hour is 3,600,000 J. The calorie here is the thermochemical calorie, exactly 4.184 J, so a kilocalorie is 4,184 J. The BTU is the International Table unit, 1,055.05585262 J. A US therm is 105,480,400 J. A foot-pound force is 0.3048 m × 4.4482216152605 N, or 1.3558179483 J. An electronvolt is exactly 1.602176634 × 10-19 J (NIST CODATA). Other factors follow NIST SP 811, Appendix B.8. Results use 8 significant digits, with whole numbers shown in full. In the panel below the converter, very large or small values use exponent form such as 5.2228948e+25, while the number boxes always keep plain digits.
Worked example: 2,000 kcal in kJ
With the default inputs the tool computes 2,000 × 4,184 ÷ 1,000 and shows 2,000 kcal = 8,368 kJ, with the reverse line 1 kJ = 0.23900574 kcal. The panel below it shows 2.3244444 kWh, 7,931.3337 BTU and 2,000,000 small calories, which is the 1,000 times gap the note under the converter warns about.
Handy equivalents
| One of this | Equals |
|---|---|
| 1 kWh | 3.6 MJ, 860.42 kcal, 3,412.1 BTU |
| 1 therm | 29.3 kWh, 105.48 MJ |
| 1 kcal | 4.184 kJ, 1.1622 Wh |
| 1 BTU | 1,055.1 J, 778.17 ft-lb |
Limits and edge cases
The international table calorie, 4.1868 J, is about 0.07 percent larger than the thermochemical one used here, which is the figure nutrition and chemistry use. The tool's BTU is the International Table BTU, the one behind the 3,412 BTU per kWh figure. Energy is not power: a kilowatt-hour measures energy used over time, while a kilowatt measures the rate. Foot-pound here is energy, not the torque unit. Negative values are accepted, for example heat released. You can type 1,250 with a thousands comma or 2,5 with a decimal comma, and a pasted 1.6e-19 becomes plain digits. Values above 1,000,000,000,000,000,000,000,000 are refused.
To turn kW into kWh, start with the power converter. To price a bill, use the electricity cost calculator. For daily food energy, try the calorie calculator, and for sizing heating or cooling, the BTU calculator.
Frequently asked questions
How many kJ are in a Calorie (kcal)?
One food Calorie, or kilocalorie, is 4.184 kJ. A 2,000 Calorie diet is 8,368 kJ.
What is the difference between a calorie and a Calorie?
A small calorie (cal) is 4.184 J. A food Calorie with a capital C is a kilocalorie (kcal), which is 1,000 small calories or 4,184 J. Nutrition labels use kilocalories, so pick kcal in the menu for food.
How many BTU are in a kWh?
One kilowatt-hour is 3,412.1416 BTU (International Table). Utilities often round this to 3,412.
How many kWh are in a therm?
A US therm is exactly 105,480,400 J, which is 29.300111 kWh. Natural gas bills use therms.
How do I convert joules to calories?
Divide joules by 4.184 to get small calories, or by 4,184 to get kilocalories. For example, 1,000 J = 239.00574 cal.
Sources: NIST SP 811, Appendix B.8 and Appendix B.9 for energy units, and NIST CODATA for the electronvolt.