Convert kilojoules to watt-hours

1 kJ=0.2778Wh

Use the converter below to change any kilojoules value into watt-hours instantly — with formula, conversion table, and real-world examples.

You have

Equals

0.27778

Conversion formula

Forward

watt-hours = kilojoules × 0.2778

Reverse

kilojoules = watt-hours × 3.6

Example: 10 kJ × 0.2778 = 2.77778 Wh.

About both units

From

Kilojoule

The kilojoule equals 1000 joules. Used on European nutrition labels (required by EU law alongside kcal), for mechanical work specifications, and some engineering contexts. A 100 g chocolate bar contains about 2100 kJ.

Real-world: 100 g chocolate: ~2100 kJ. EU daily intake (adult): ~8400 kJ. Tesla Model 3 battery: ~270 MJ = 270,000 kJ.

Read full kilojoule reference →

Watt-Hour

The watt-hour equals 3600 joules — 1 W delivered for 1 hour. Used for phone, laptop and small-battery capacities. A typical smartphone battery is 10–20 Wh; a laptop is 50–100 Wh.

Real-world: iPhone battery: 12 Wh. MacBook Pro: 70 Wh. Power bank: 20 Wh–100 Wh. Airplane carry-on limit: usually 100 Wh.

Read full watt-hour reference →

Kilojoule to Watt-Hour conversion table

Common kilojoules to watt-hours values for quick reference.

Kilojoule (kJ)	Watt-Hour (Wh)
1 kJ	0.2778 Wh
10 kJ	2.77778 Wh
100 kJ	27.7778 Wh
500 kJ	138.889 Wh
1,000 kJ	277.778 Wh
5,000 kJ	1,388.89 Wh
10,000 kJ	2,777.78 Wh
50,000 kJ	13,888.89 Wh
100,000 kJ	27,777.78 Wh
500,000 kJ	138,888.89 Wh

Tips & common mistakes

Quick tips

1 kJ = 1000 J = 0.239 kcal.
EU nutrition labels must show both kJ and kcal.
For quick conversion: kcal × 4.2 = kJ.

Avoid these

Assuming European labels use kcal only — they use both kJ and kcal.
Confusing kJ with kW (power).
Using kcal when kJ is requested in scientific context.

Frequently asked questions

How many watt-hours in a kilojoule?

One kilojoule equals 0.2778 watt-hours.

How do I convert kilojoules to watt-hours?

Multiply the kilojoule value by 0.2778 to get the equivalent in watt-hours.

What is 100 kilojoules in watt-hours?

100 kilojoules equals 27.7778 watt-hours.

Is a kilojoule bigger than a watt-hour?

No. 1 kilojoule equals 0.2778 watt-hours, so one kilojoule is smaller.

How to convert kilojoules to watt-hours without a calculator?

Multiply by 0.28 for a quick estimate; use a calculator for precise results.

Related energy conversions

📊 See full comparison matrix →

Conversions in other categories

WeightKilogram → Pound LengthKilometer → Mile TemperatureCelsius → Fahrenheit VolumeLiter → US Gallon AreaSquare Meter → Square Foot SpeedKilometer per Hour → Mile per Hour PressureBar → Pound per Square Inch PowerKilowatt → Mechanical Horsepower