This energy converter bridges the two worlds that measure energy differently: food (calories, kilocalories) and physics/electricity (joules, kilowatt-hours, BTU) — all convertible both ways.
One Energy, Many Currencies
The joule is physics' unit; the kilocalorie (the "Calorie" on food labels, capital C) is biology's — 1 kcal = 4,184 J exactly by definition. The kWh is electricity billing: 3.6 million joules delivered over an hour at a kilowatt. The BTU heats buildings in the US. A single converter spans them because your body, your kettle and your furnace all run on the same physics. What the electricity costs, though, is our Electricity Cost Calculator's department. Part of our Conversion Calculators collection.
Quick Reference
| 1 unit | = joules | = kcal |
|---|---|---|
| 1 kcal (food Calorie) | 4,184 | 1 |
| 1 kWh | 3,600,000 | 860.4 |
| 1 BTU | 1,055.1 | 0.252 |
| 1 ft·lb | 1.356 | 0.000324 |
Worked Examples (Verified)
- 1 kWh = 860.4 kcal — boiling a kettle for an hour is, energetically, a large meal; your body just spends it slower
- A 500 kcal lunch = 2.09 megajoules = 0.58 kWh — at typical electricity prices, your lunch "contains" about 8 cents of grid energy (digestion's markup is the business model of restaurants)
- A 10,000 BTU air conditioner moves 10.55 MJ of heat per hour ≈ 2.93 kW of cooling
Related Tools
- Electricity Cost Calculator — kWh into dollars
- Power Converter — energy per unit time
- Conversion Calculators — the full collection
Frequently Asked Questions
How many joules are in a calorie?
A small calorie (cal) is 4.184 J; a food Calorie (kcal) is 1,000 of those — 4,184 J. The capitalization swindle on food labels trips everyone once.
How many kcal are in a kWh?
860.4 kcal. The conversion 1 kWh = 3.6 MJ is exact (a kilowatt for 3,600 seconds); dividing by 4,184 J/kcal gives the food-energy equivalent.
What is a BTU in joules?
1 BTU ≈ 1,055 J — the energy to raise a pound of water by 1°F, and the unit behind US furnace and AC ratings (a "10,000 BTU" AC moves that much heat per hour).
Why do food labels say Calories but kj elsewhere?
Convention by region: the US uses kcal ("Calories"), the EU and Australia list kJ (and often both). A 500 kcal item reads 2,092 kJ — same lunch, different currency.
Is a kWh energy or power?
Energy: kilowatt (power) × hours (time). A 100 W bulb running 10 hours uses exactly 1 kWh — the Power Converter handles the rate side of the family.
Is this energy converter free?
Yes — free, instant, no sign-up.