What this tool does
Converts between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and electron volts.
Converter and calculator
Energy Converter
Convert between joules, calories, kilocalories, watt-hours, BTU, kilowatt-hours, and more. Covers physics, nutrition, and engineering use cases.
Complete guide
How to use Energy Converter
Unit converters guide for energy converter users.
Energy is measured in different units depending on the field: joules in physics, calories in chemistry, kilocalories (kcal) in nutrition, kilowatt-hours (kWh) on electricity bills, and BTU in HVAC. This converter handles them all.
A common point of confusion: the 'calorie' on food labels is actually a kilocalorie (1 food Calorie = 1,000 chemistry calories = 4,184 joules).
Food Calories vs calories
1 food Calorie (Cal) = 1 kilocalorie (kcal) = 4,184 joules. The capital C distinguishes food energy from chemistry calories.
How to use it
Enter a value and select the source unit. All target units update immediately.
Quick checklist
- Food labels use kcal (kilocalories), often written as 'Calories' with a capital C.
- 1 kWh = 3,600,000 joules = 3.6 MJ.
- 1 BTU = 1,055 joules — used in HVAC and heating systems.
- For electricity cost: your bill is in kWh; 1 kWh is the energy to run a 1,000W device for 1 hour.
Answers
Energy Converter FAQs
How many joules in a calorie?
1 thermochemical calorie = 4.184 joules. 1 food Calorie (kcal) = 4,184 joules.
What is a kilowatt-hour?
1 kWh = the energy used by a 1,000W device running for 1 hour = 3,600,000 joules.
How many calories in a BTU?
1 BTU = 251.996 thermochemical calories = 0.252 kcal.
What unit does my electricity bill use?
Kilowatt-hours (kWh). Multiply kWh by your rate per kWh to get the cost.