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Energy Converter
Convert energy between joules, calories, watt-hours, kilowatt-hours and BTU.
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How to Use This Converter
Type a value in either box and pick the units. The other box updates instantly. Use the swap button to reverse the direction.
- All 9 units are supported in both directions.
- Results update live as you type — no button to press.
- Values are formatted for readability while staying precise.
Frequently Asked Questions
How do I convert kWh to joules?
Multiply by 3.6 million. 1 kWh = 3,600,000 J.
What is the difference between a calorie and a food calorie?
A food calorie (kcal) is 1,000 scientific calories. This converter treats "cal" as the scientific unit.
What is a BTU?
The British Thermal Unit — the energy to raise 1 lb of water by 1°F. Used for heating and cooling.
How many kWh does a 100 W bulb use in 10 hours?
1 kWh — 100 W × 10 h = 1,000 Wh = 1 kWh.
Practical Example
Convert 1 kilowatt-hour to joules. Because 1 W = 1 joule per second, 1 kWh = 1,000 W × 3,600 s = 3,600,000 J.
- 3,600,000 J ÷ 4.184 = 860,421 scientific calories ≈ 860.4 kcal
- 3,600,000 J ÷ 1,055.06 = 3,412 BTU
- So a typical household daily use of 30 kWh = 108 million joules
What Your Results Mean
- Joules (J) — the SI unit of energy; 1 J = 1 watt-second.
- Kilowatt-hours (kWh) — the unit on electricity bills; 1 kWh = 3.6 MJ.
- Calories (cal) — 1 cal = 4.184 J; a food "calorie" is actually 1 kcal = 1,000 cal.
- BTU — energy to heat 1 lb of water by 1°F; 1 BTU ≈ 1,055 J.
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