Home› Conversions› Energy› Joules to Watt-hours
Energy
Joules to Watt-hours
Convert joules (J) to watt-hours (Wh). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 J = 0.000278 Wh
Joules to Watt-hours Conversion Table
Common values, ready to copy:
| joules | watt-hours |
|---|---|
| 1 J | 0.000278 Wh |
| 2 J | 0.000556 Wh |
| 5 J | 0.001389 Wh |
| 10 J | 0.002778 Wh |
| 25 J | 0.006944 Wh |
| 50 J | 0.013889 Wh |
| 100 J | 0.027778 Wh |
| 1,000 J | 0.277778 Wh |
Formula
watt-hours = joules × 2.77777778e-4
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
About Joules and Watt-hours
Joules (J): The SI unit of energy; named for James Prescott Joule, whose 19th-century experiments established the equivalence of mechanical work and heat. Common uses: Physics calculations, food calorie labeling in metric countries (kilojoules), battery capacity, and chemistry.
Watt-hours (Wh): The energy consumed by a 1-watt device in 1 hour; equals 3,600 joules. Common uses: Small battery capacities (laptop batteries are typically 40-100 Wh), and lighting energy use.
How the conversion works
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
The exact relationship is watt-hours = joules × 2.77777778e-4, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.
When this conversion matters
Converting between joules and watt-hours comes up wherever energy measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.