Energy Converter
Convert between joules, calories, kilowatt-hours, BTU, therms, electron volts, and more. Includes food calorie vs physics calorie explanation and gas bill reference.
Convert units on your UK gas bill to kWh.
How to use this tool
- 1Find the unit you know
Locate the input field for the energy unit you have — joules, calories, kWh, BTU, therms, electron volts, or any of the 13 supported units.
- 2Type the value
Enter your number into the field. All other unit fields update instantly — no button click needed.
- 3Copy or compare
Click the copy button next to any value. Check the reference section for real-world energy comparisons like food calories and gas bill conversions.
Understanding energy units
Joules & kilowatt-hours
The joule (J) is the SI unit of energy. For everyday electricity use, the kilowatt-hour (kWh) is more practical — it equals 3.6 million joules and is the standard billing unit on electricity bills worldwide. One kWh powers a 100-watt bulb for 10 hours.
Calories vs food Calories
The physics calorie (cal) equals 4.184 joules. The food Calorie (kcal, written with capital C) equals 4,184 joules — one thousand times larger. A slice of bread contains about 80 kcal (80,000 cal). This distinction trips up many students and health-conscious consumers alike.
BTU & therms
The British Thermal Unit (BTU) is used to rate heating and cooling equipment. One BTU = 1,055 joules. A therm equals 100,000 BTU and is used on UK gas bills. One therm = 29.307 kWh, which makes it easy to compare gas and electricity costs.
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