What this energy converter does
Energy shows up in many units depending on the field. Physicists and engineers use joules, nutrition labels use food Calories, heating and air-conditioning equipment is rated in BTU, and electricity bills are measured in kilowatt-hours. This converter switches between four of them: joules, calories, BTU and kWh. It multiplies your value by the conversion factor for the starting unit, expressed in joules, and divides by the factor for the target unit.
Use it to estimate what a kilowatt-hour of electricity means in heating terms, to compare a furnace rating in BTU with an electric heater, to check a chemistry answer given in joules against a table in calories, or to put a snack in perspective against a workout. Note that "calories" here means the small thermochemical calorie, exactly 4.184 J. A food Calorie (capital C) is 1,000 of these, so it equals a kilocalorie.
Conversion factors and method
result = value × factor(from) ÷ factor(to)
- 1 joule = 1 J (the base unit used internally).
- 1 calorie = 4.184 J (thermochemical calorie).
- 1 BTU = 1055.06 J (the International Table BTU, about 1055 J).
- 1 kWh = 3,600,000 J, since one kilowatt is 1,000 J per second and an hour is 3,600 seconds.
The answer is shown rounded to six decimal places with the target unit appended, so very small results may display as 0.000000. In that case convert to a smaller unit instead.
Worked example
Convert 1 kWh to BTU. Value in joules: 1 × 3,600,000 = 3,600,000 J. Divide by the BTU factor: 3,600,000 / 1055.06 = 3412.13 BTU. So a kilowatt-hour of electrical energy is about 3,412 BTU, which is why a 1,500 W space heater delivers roughly 5,118 BTU per hour. A second check: 100 calories to joules is 100 × 4.184 / 1 = 418.4 J. The calculator prints 3412.128220 BTU and 418.400000 joules for these inputs.
Common mistakes and how to interpret the result
- Confusing calories and Calories. Food labels list kilocalories. To convert 200 food Calories, enter 200,000 calories.
- Mixing energy and power. BTU is energy, while BTU per hour, watts and horsepower measure power. Do not convert kWh to watts directly.
- Assuming there is one BTU. Several BTU definitions differ by a fraction of a percent. This tool uses 1055.06 J, which is fine for everyday work but not for precision thermodynamics.
- Ignoring efficiency. The converter changes units only. A gas furnace delivering 1 kWh of heat does not use 1 kWh of fuel energy.