Kilojoules to Watt Hours Converter

Kilojoules to Watt Hours

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

The Formula

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

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

Conversion Table

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

The Other Direction

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

What Each Unit Is

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

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

A Sense of Scale

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

Precision

The factor 0.277777777778 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 kilojouleToWattHour = (value) => value * 0.277777777778; ``

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 kJ with the factor truncated at each decimal place:

Decimals kept	Factor	137 kJ becomes	Error
0	0	0	100.0000%
1	0.3	41.1	8.0000%
2	0.28	38.36	0.8000%
3	0.278	38.086	0.0800%
4	0.2778	38.0586	0.0080%

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 kilojoules to three significant figures, the answer in watt hours is only good to three — writing more digits claims precision the measurement never had.

Other Conversions From Kilojoules

The same value in every other unit this converter supports for energy:

From	To	Unit
1 kJ	1,000 J	Joules
1 kJ	239.006 cal	Calories
1 kJ	0.239006 kcal	Kilocalories
1 kJ	2.7778e-4 kWh	Kilowatt Hours
1 kJ	0.947817 BTU	BTU

Chaining conversions works — kilojoules to metres to feet gives the same answer as kilojoules to feet — but each step rounds, so a chain of three conversions carries three roundings. Convert directly where a direct factor exists.