Joules to Kilojoules Converter

Joules to Kilojoules

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

The Formula

`` kilojoules = joules × 0.001 joules = kilojoules × 1000 `

One joule is 0.001 kilojoules, and one kilojoule is 1,000 joules.

Conversion Table

Joules	Kilojoules
1 J	0.001 kJ
2 J	0.002 kJ
5 J	0.005 kJ
10 J	0.01 kJ
25 J	0.025 kJ
50 J	0.05 kJ
100 J	0.1 kJ
500 J	0.5 kJ
1,000 J	1 kJ

The Other Direction

Kilojoules	Joules
1 kJ	1,000 J
2 kJ	2,000 J
5 kJ	5,000 J
10 kJ	10,000 J
25 kJ	25,000 J
50 kJ	50,000 J
100 kJ	100,000 J
500 kJ	500,000 J
1,000 kJ	1,000,000 J

What Each Unit Is

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.

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

A Sense of Scale

• Lifting an apple one metre takes about 1 J
• A heartbeat uses roughly 1 J
• An apple holds about 400 kJ
• Daily intake is around 8,700 kJ

Precision

The factor 0.001 is exact by international agreement, not a rounded approximation. Any imprecision in a result comes from your input, not the conversion.

In Code

`javascript const jouleToKilojoule = (value) => value * 0.001; ``

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 J with the factor truncated at each decimal place:

Decimals kept	Factor	137 J becomes	Error
0	0	0	100.0000%
1	0	0	100.0000%
2	0	0	100.0000%
3	0.001	0.137	—
4	0.001	0.137	—

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

Other Conversions From Joules

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

From	To	Unit
1 J	0.239006 cal	Calories
1 J	2.3901e-4 kcal	Kilocalories
1 J	2.7778e-4 Wh	Watt Hours
1 J	2.7778e-7 kWh	Kilowatt Hours
1 J	9.4782e-4 BTU	BTU

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