Convert kWh to joules and other energy units: complete guide
Convert energy units: kWh, joules, calories, BTU. Reference table and electrical consumption examples.
Published on January 14, 2026Energy units appear everywhere: electricity bills (kWh), nutrition (kcal), thermodynamics (joules), heating (BTU). Understanding the conversions between these units is useful for comparing electrical appliances, calculating energy savings or solving physics problems.
Understanding the conversion
The joule (J) is the SI unit of energy. The kilowatt-hour (kWh) is the practical unit for electricity: 1 kWh = the energy supplied by a power of 1 kW for 1 hour = 3,600,000 joules. The calorie (cal) and kilocalorie (kcal) measure food energy: 1 kcal = 4,186 joules. The BTU (British Thermal Unit) is used in Anglo-Saxon heating/air conditioning systems.
📐 Formula
📊 Conversion table
| Unit | Equivalent in joules | Equivalent in kWh | Domain |
|---|---|---|---|
| 1 joule (J) | 1 J | 2.78 × 10⁻⁷ kWh | Physics, SI |
| 1 kilojoule (kJ) | 1,000 J | 2.78 × 10⁻⁴ kWh | Nutrition, chemistry |
| 1 calorie (cal) | 4.186 J | — | Physics (historical) |
| 1 kilocalorie (kcal) | 4,186 J | 1.16 × 10⁻³ kWh | Food/nutrition |
| 1 kWh | 3,600,000 J | 1 kWh | Electricity |
| 1 BTU | 1,055 J | 2.93 × 10⁻⁴ kWh | Heating (US/UK) |
| 1 MWh | 3.6 × 10⁹ J | 1,000 kWh | Industry, grid |
💡 Practical examples
An oven at 2,000 W (2 kW) used for 30 min: energy = 2 kW × 0.5 h = 1 kWh = 3,600,000 J. At $0.15/kWh, cost = $0.15.
A 700 kcal meal = 700 × 4,186 = 2,930,200 J = 0.814 kWh. The human body consumes about 2,000 kcal/day ≈ 2.33 kWh of 'fuel'.
4,000 mAh battery at 3.7V: energy = 4 × 3.7 = 14.8 Wh = 0.0148 kWh = 53,280 J ≈ 53 kJ.