Energy Converter
Convert between joules, calories, kilowatt-hours, BTU, and foot-pounds.
How energy conversion works
Every energy unit here converts through the joule — the SI base unit of energy. The units on food labels (Calories, capitalized) are actually kilocalories, a source of frequent confusion: one food 'Calorie' equals 1,000 small calories, and both are defined as the energy needed to raise a specific amount of water by 1°C.
Common conversions
- 1 food Calorie (kcal) ≈ 4,184 joules ≈ 4.184 kJ
- 1 kilowatt-hour = 3,600,000 joules — the unit your electricity bill is measured in
- 1 BTU ≈ 1,055 joules ≈ 0.252 kcal
- A typical adult diet is often around 2,000 kcal/day ≈ 8,368 kJ/day
Frequently asked questions
Why does 'Calorie' on food labels mean kilocalorie?
It's a long-standing labeling convention: the capital-C 'Calorie' used in nutrition is always a kilocalorie (1,000 small calories), while the lowercase 'calorie' used in chemistry and physics is the smaller unit. Both units appear in casual use, which is why they get confused.
Why is my electricity bill in kilowatt-hours instead of joules?
A kilowatt-hour is a far more practically sized unit for household energy use — a single joule is a tiny amount of energy (about what it takes to lift an apple one meter), so measuring a month of electricity use in joules would mean dealing with numbers in the billions.