The formula
J = kWh × 3,600,000
Where the factor comes from — each unit by its definition, then its size in SI:
1 kWh = 1000 × Wh = 3,600,000 J1 J is the SI unit of energy.
Dividing the two SI sizes gives the factor: 3,600,000, exact — every step above is a definition, not a measurement. The reverse factor is 2.77777777778 × 10⁻⁷.
The SI unit of energy is the joule. Food labels use kilocalories, electricity bills kilowatt-hours, heating specs BTU and particle physics electronvolts — the same quantity in five costumes.
Worked examples
- A day's food (2000 kcal): 2.32444 kWh = 8,368,000 J — 2.32444 × 3,600,000 = 8,368,000
- A 1 kW heater run for one hour: 1 kWh = 3,600,000 J — 1 × 3,600,000 = 3,600,000
- Lifting 1 kg through 1 m at standard gravity: 2.72407 × 10⁻⁶ kWh = 9.80665 J — 2.72407 × 10⁻⁶ × 3,600,000 = 9.80665
- A visible-light photon (2 eV): 8.90098 × 10⁻²⁶ kWh = 3.20435 × 10⁻¹⁹ J — 8.90098 × 10⁻²⁶ × 3,600,000 = 3.20435 × 10⁻¹⁹
Frequently asked questions
How many joules is 1 kWh?
1 kWh = 3,600,000 J, exactly, from the unit definitions.
How do I convert joules back to kilowatt-hours?
Divide by 3,600,000 — or multiply by 2.77777777778 × 10⁻⁷: 1 J = 2.77777777778 × 10⁻⁷ kWh.