Kilojoules to Joules Converter

Kilojoules to Joules

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

The Formula

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

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

Conversion Table

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

The Other Direction

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

What Each Unit Is

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

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

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

Precision

The factor 1000 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 kilojouleToJoule = (value) => value * 1000; ``

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	1000	137,000	—
1	1000	137,000	—
2	1000	137,000	—
3	1000	137,000	—
4	1000	137,000	—

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 joules 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	239.006 cal	Calories
1 kJ	0.239006 kcal	Kilocalories
1 kJ	0.277778 Wh	Watt Hours
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.