Energy Unit Converter — Joules, Calories, kWh, BTU and More
Convert energy units instantly — joules, calories, kilowatt-hours, BTU, electron volts, and more. Includes real-world examples and a complete reference table.
Energy shows up in wildly different units depending on who's measuring it and why. A nutritionist talks about calories. A physicist uses joules. An electrician works in kilowatt-hours. A HVAC engineer specifies BTU. A chemist might use electron volts. They're all measuring the same thing — just with different scales designed for different purposes.
The CalcHub energy converter converts between all of them without requiring you to know the conversion factors off the top of your head.
Energy Conversion Reference Table
| From | To | Multiply by |
|---|---|---|
| 1 joule (J) | calories (cal) | 0.239006 |
| 1 joule (J) | kilocalories (kcal) | 0.000239006 |
| 1 calorie (cal) | joules (J) | 4.184 |
| 1 kilocalorie (kcal) | joules (J) | 4184 |
| 1 kilowatt-hour (kWh) | joules (J) | 3,600,000 |
| 1 kilowatt-hour (kWh) | kilocalories | 859.845 |
| 1 BTU | joules (J) | 1055.06 |
| 1 BTU | kilocalories | 0.251996 |
| 1 BTU | watt-hours | 0.293071 |
| 1 kWh | BTU | 3412.14 |
| 1 electron volt (eV) | joules (J) | 1.602 × 10⁻¹⁹ |
The Calorie Confusion
Here's something that trips up nearly everyone: there are two kinds of calories.
A small calorie (cal) is the amount of energy needed to raise 1 gram of water by 1°C. A large Calorie (kcal or Cal with capital C) is 1,000 small calories — the unit used in nutrition.
When a food label says a cookie has "150 Calories," it means 150 kcal, which is 150,000 small calories. The food industry almost universally uses kcal and calls them "Calories" (capital C) to avoid this confusion, but it persists anyway.
Energy Contexts Across Different Fields
Nutrition: A typical adult requires about 2,000–2,500 kcal per day. That's 8,368,000–10,460,000 joules — which sounds absurd, which is why nutritionists don't use joules. Electricity: Your power bill is measured in kWh. A 60W light bulb left on for 10 hours uses 0.6 kWh. Running an air conditioner (1,500W) for 8 hours uses 12 kWh. At $0.15 per kWh, that's $1.80 a day. HVAC: Air conditioner capacity and heat output is rated in BTU per hour (BTU/h) in the US. A 10,000 BTU/h window AC can cool roughly a 450 sq ft room. In Europe, the same equipment is rated in watts (1,000 BTU/h ≈ 293 watts). Physics and engineering: Joules and kilojoules are the SI standard. Explosive yield is sometimes given in tons of TNT (1 ton TNT = 4.184 × 10⁹ J). Nuclear yields use megatons (1 megaton TNT = 4.184 × 10¹⁵ J).How to Use the CalcHub Energy Converter
- Go to calchub.in and open the Energy Converter
- Enter your energy value
- Choose the source unit from the dropdown
- The result appears across all supported energy units at once
Practical Energy Reference
| Activity / Object | Energy |
|---|---|
| One food Calorie (kcal) | 4,184 joules |
| A chocolate bar (~250 kcal) | ~1,045,000 joules |
| Average US home daily electricity use | ~30 kWh |
| Energy in 1 liter of gasoline | ~34.2 MJ (about 9.5 kWh) |
| 1 stick of dynamite | ~2.1 MJ |
| Hiroshima atomic bomb | ~63 TJ (63 × 10¹² J) |
Why does the US use BTU instead of joules?
BTU (British Thermal Unit) became the standard in US heating and cooling industries before the metric system was widely adopted in science and engineering. Since building codes, appliance ratings, and industry standards all used BTU, it stuck — even though the British stopped using it.
What's the difference between power and energy?
Energy is the total amount of work done or heat transferred — measured in joules or kWh. Power is the rate at which energy is used — measured in watts (joules per second) or horsepower. A 100W bulb burning for 1 hour uses 0.1 kWh of energy. Power × Time = Energy.
How do I convert food calories burned during exercise to kWh?
Divide by 860. Running 500 kcal worth of exercise is about 0.58 kWh of energy. For context, that's enough electricity to run a 60W bulb for almost 10 hours. The human body is impressively inefficient — only about 25% of food energy actually goes to movement.
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