Watt Hours to Joules Converter

Watt Hours to Joules

Convert watt hours (Wh) to joules (J). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.

The Formula

`` joules = watt hours × 3600 watt hours = joules × 0.000277777777778 `

One watt hour is 3,600 joules, and one joule is 2.7778e-4 watt hours.

Conversion Table

Watt Hours	Joules
1 Wh	3,600 J
2 Wh	7,200 J
5 Wh	18,000 J
10 Wh	36,000 J
25 Wh	90,000 J
50 Wh	180,000 J
100 Wh	360,000 J
500 Wh	1,800,000 J
1,000 Wh	3,600,000 J

The Other Direction

Joules	Watt Hours
1 J	2.7778e-4 Wh
2 J	5.5556e-4 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
500 J	0.138889 Wh
1,000 J	0.277778 Wh

What Each Unit Is

Watt Hours (Wh) — one watt sustained for one hour, or 3,600 joules. The practical electrical energy unit, following the adoption of the watt.

Joules (J) — the work done by one newton acting over one metre — the SI derived unit of energy. Named for James Prescott Joule, who established the mechanical equivalent of heat.

A Sense of Scale

• A phone battery holds 12–20 Wh
• A laptop battery is 50–100 Wh
• Lifting an apple one metre takes about 1 J
• A heartbeat uses roughly 1 J

Precision

The factor 3600 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.

In Code

`javascript const wattHourToJoule = (value) => value * 3600; ``

Where This Conversion Comes Up

• Nutrition
• Electricity
• Fitness
• Heating
• Fuel

How Many Decimals Do You Need?

Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 Wh with the factor truncated at each decimal place:

Decimals kept	Factor	137 Wh becomes	Error
0	3600	493,200	—
1	3600	493,200	—
2	3600	493,200	—
3	3600	493,200	—
4	3600	493,200	—

A rule that holds for any conversion: round once, at the end. Rounding the factor and then multiplying compounds the error through every subsequent calculation, while carrying full precision and rounding the final answer does not.

The right number of significant figures is set by your input, not by the converter. If you measured watt hours to three significant figures, the answer in joules is only good to three — writing more digits claims precision the measurement never had.