How to Convert Watt-hours to Joules (Wh to J)
Energy conversions link food labels in kJ and kcal, SP Group bills in kWh and air-conditioner capacity in BTU. This guide shows how to convert watt-hours into joules by hand, with examples and a quick-reference table.
The conversion
To convert watt-hours to joules, multiply the value by 3,600. To go the other way, divide by the same number (or multiply by 0.0002777778). For a quick estimate, multiply by about 3,600.
Joules = watt-hours × 3,600
Worked examples
- 3 Wh = 10,800 J
- 12.5 Wh = 45,000 J
- 75 Wh = 270,000 J
Watt-hours to Joules table
| Watt-hours | Joules |
|---|---|
| 1 Wh | 3,600 J |
| 2 Wh | 7,200 J |
| 5 Wh | 18,000 J |
| 10 Wh | 36,000 J |
| 20 Wh | 72,000 J |
| 25 Wh | 90,000 J |
| 50 Wh | 180,000 J |
| 100 Wh | 360,000 J |
| 250 Wh | 900,000 J |
| 500 Wh | 1,800,000 J |
| 1,000 Wh | 3,600,000 J |
Common questions
Is Wh to J exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Joules to Watt-hours converter.
Mistakes to avoid
Rounding the factor too early
Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.
Forgetting squared and cubed units
Area and volume factors are the length factor squared or cubed, so 1 m² is about 10.76 sq ft, not 3.28.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
Background
Many conversion factors are exact by definition. The inch has been defined as exactly 2.54 centimetres since 1959, and the pound as exactly 0.45359237 kilograms, so conversions involving them can be as precise as you need.
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
For any value, use the Watt-hours to Joules Converter or browse all energy converters.
Run your own numbers: Watt-hours to Joules Converter