Watt Hours to Kilojoules Converter

Watt Hours to Kilojoules

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

The Formula

`` kilojoules = watt hours × 3.6 watt hours = kilojoules × 0.277777777778 `

One watt hour is 3.6 kilojoules, and one kilojoule is 0.277778 watt hours.

Conversion Table

Watt Hours	Kilojoules
1 Wh	3.6 kJ
2 Wh	7.2 kJ
5 Wh	18 kJ
10 Wh	36 kJ
25 Wh	90 kJ
50 Wh	180 kJ
100 Wh	360 kJ
500 Wh	1,800 kJ
1,000 Wh	3,600 kJ

The Other Direction

Kilojoules	Watt Hours
1 kJ	0.277778 Wh
2 kJ	0.555556 Wh
5 kJ	1.3889 Wh
10 kJ	2.7778 Wh
25 kJ	6.9444 Wh
50 kJ	13.8889 Wh
100 kJ	27.7778 Wh
500 kJ	138.8889 Wh
1,000 kJ	277.7778 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.

Kilojoules (kJ) — 1,000 joules. The metric food-energy unit outside North America.

A Sense of Scale

• A phone battery holds 12–20 Wh
• A laptop battery is 50–100 Wh
• An apple holds about 400 kJ
• Daily intake is around 8,700 kJ

Doing It in Your Head

Multiply by 11, then divide by 3. That is off by 1.85% — close enough to judge a distance, a weight or a price, and not close enough to sign off on a drawing.

Exact	Mental shortcut
36 kJ	36.6667 kJ
360 kJ	366.6667 kJ

Precision

The factor 3.6 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 wattHourToKilojoule = (value) => value * 3.6; ``

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	4	548	11.1111%
1	3.6	493.2	—
2	3.6	493.2	—
3	3.6	493.2	—
4	3.6	493.2	—

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 kilojoules is only good to three — writing more digits claims precision the measurement never had.