Energy Converter
One calorie equals exactly 4.184 joules, and one food Calorie (kilocalorie) is 4,184 joules or 4.184 kJ. One kilowatt-hour is 3.6 million joules, about 3,412 BTU. This energy converter switches between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU as you type.
1 kcal = 4.184 kJ
How to use the Energy Converter
- Type an amount of energy in the From box. It starts at 500 kcal.
- Choose the From and To units, for example kcal and kJ.
- Read the result in the To box, or type there to convert the other way.
- Use the swap button to reverse the units, and the chips to see the value in every other unit.
Formula
result = value × (from-unit in J) ÷ (to-unit in J)All units convert through joules: 1 kJ = 1,000 J, 1 cal = 4.184 J (thermochemical calorie), 1 kcal = 4,184 J, 1 Wh = 3,600 J, 1 kWh = 3,600,000 J and 1 BTU = 1,055.05585 J (International Table BTU).
Common energy conversions
- 1 kcal = 4.184 kJ
- 1 kJ = 0.239 kcal
- 1 kWh = 3,600 kJ = 3,412 BTU
- 1 BTU = 1.055 kJ = 0.000293 kWh
- 1 Wh = 3,600 J
Where each unit is used
- Joules (J) and kilojoules (kJ): physics, and food labels in Australia and Europe
- Kilocalories (kcal, food Calories): nutrition labels and diet planning
- Calories (cal): chemistry and older scientific literature
- Watt-hours and kilowatt-hours: batteries and electricity bills
- BTU: heating, air conditioning and gas appliances
Energy Converter questions
How do I convert calories to joules?
Multiply calories by 4.184 to get joules. For example, 100 cal is 418.4 J. For food energy, multiply kilocalories by 4.184 to get kilojoules: a 250 kcal snack is 1,046 kJ. Be sure which calorie you have, because the food Calorie is 1,000 times larger.
What is the difference between a calorie and a food Calorie?
A food Calorie, written with a capital C or as kcal, equals 1,000 small calories, or 4.184 kJ. Nutrition labels use kilocalories, while chemistry uses the small calorie. Mixing them up produces an error of exactly 1,000 times. Food labels in Australia and Europe often show kilojoules alongside kilocalories.
How many BTU are in a kilowatt-hour?
One kilowatt-hour is about 3,412 BTU, and one BTU is about 0.000293 kWh. This conversion is used to compare electric and gas heating, and to size air conditioners. Real systems also lose some energy, so efficiency changes the delivered amount.
Should I use joules or calories for exercise physiology?
Use kilocalories when talking about food and daily energy expenditure, and joules for physics-based calculations such as mechanical work and power. Exercise science often uses METs, where 1 MET is about 1 kcal per kilogram per hour. Research papers usually report in kilojoules to stay consistent with SI units.
How do I turn energy into power?
Divide energy in joules by time in seconds to get power in watts. For example, burning 100 kcal (418,400 J) in 30 minutes (1,800 s) averages 232 W of metabolic power. One watt is one joule per second. Multiply power by time to go back from watts to joules.
What are common energy conversion mistakes?
The most common mistakes are confusing cal with kcal and mixing up energy (kWh) with power (kW). Use exact factors (1 cal = 4.184 J, 1 kWh = 3.6 MJ) and keep units consistent through a calculation before rounding the final answer.
How much energy does a typical household use?
A typical US household uses about 10,500 kWh of electricity a year, around 29 kWh a day, while many European homes use 3,000 to 4,500 kWh a year. Multiply kWh by 3.6 to express the total in megajoules. Your electricity bill shows your actual monthly use in kWh.