Kilojoules to Joules Converter

Convert kilojoules to joules instantly with our free energy conversion calculator. Enter any value for accurate results.

How to Convert Kilojoules to Joules

To convert an energy measurement from kilojoules to joules, multiply the energy value by the conversion factor. Since one kilojoule is equal to 1,000 joules, you can use this formula:

joules = kilojoules × 1,000

The energy in joules is equal to the kilojoules multiplied by 1,000.

Example: Convert 5 kilojoules to joules.

Using the formula: joules = kilojoules × 1,000

joules = 5 kJ × 1,000 = 5,000 J

Therefore, 5 kilojoules equals 5,000 joules.

How Many Joules Are in a Kilojoule?

There are 1,000 joules in one kilojoule.

1 kJ = 1,000 J

What Is a Kilojoule?

The kilojoule (symbol: kJ) is a metric unit of energy equal to one thousand (10³) joules. The prefix “kilo” denotes a factor of 1,000 in the International System of Units. Kilojoules are commonly used in nutrition, particularly in Australia, New Zealand, and the European Union, to express the energy content of foods on packaging labels. In these regions, food energy is typically shown in kilojoules alongside or instead of kilocalories. A typical adult requires about 8,000–10,000 kJ (roughly 2,000–2,500 kilocalories) of food energy per day. A slice of bread contains about 300–400 kJ, a banana about 350–450 kJ, and a typical fast-food burger about 2,000–3,000 kJ. The kilojoule is also used in chemistry to express bond energies, reaction enthalpies, and activation energies. For example, the bond energy of a carbon-carbon single bond is about 346 kJ/mol, and the bond energy of a C=C double bond is about 614 kJ/mol.

One kilojoule is equal to:

1,000 joules (J)
239.006 calories (cal)
0.239006 kilocalories (kcal)
0.277778 watt-hours (Wh)
0.947817 BTU
6.2415 × 10²¹ electronvolts (eV)

What Is a Joule?

The joule (symbol: J) is the SI derived unit of energy, named after the English physicist James Prescott Joule. It is defined as the energy transferred to an object when a force of one newton acts on it over a distance of one metre (1 J = 1 N·m = 1 kg·m²/s²). The joule is also equivalent to the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second (1 J = 1 W·s). This relationship connects the joule to both mechanical and electrical energy. As the fundamental SI energy unit, the joule is used across all branches of science and engineering. It appears in mechanics (work and kinetic energy), thermodynamics (heat transfer), electricity (electrical energy), chemistry (bond energies and reaction enthalpies), and radiation physics (photon energies). In everyday life, the joule is a relatively small unit of energy. Lifting a medium-sized apple (about 100 g) one metre against gravity requires approximately one joule. A 100-watt light bulb consumes 100 joules per second, and a typical adult requires about 8–10 million joules (8–10 MJ) of food energy per day.

One joule is equal to:

0.001 kilojoules (kJ)
0.239006 calories (cal)
0.000239006 kilocalories (kcal)
0.000277778 watt-hours (Wh)
1 watt-second (Ws)
0.000947817 BTU
6.2415 × 10¹⁸ electronvolts (eV)

Understanding Energy Units

Energy is a fundamental physical quantity that represents the capacity to do work or produce heat. It is conserved in all physical processes (the first law of thermodynamics) and can be converted from one form to another — mechanical, thermal, electrical, chemical, nuclear, and radiant energy are all interconvertible.

The wide variety of energy units reflects the historical development of different branches of science and engineering, each of which developed its own preferred units before the adoption of the International System of Units (SI).

Major Unit Families

SI / Metric units: The joule (J) is the SI unit of energy, with standard metric prefixes (kJ, MJ, GJ). The watt-second (Ws) is identical to the joule. Watt-hours (Wh), kilowatt-hours (kWh), and megawatt-hours (MWh) combine power (watts) with time.
Calorie-based units: The calorie (cal), kilocalorie (kcal), and megacalorie (Mcal) originated in thermochemistry. The kilocalorie is widely used in nutrition as the “food Calorie.”
British / Imperial units: The British thermal unit (BTU) and its multiples (MMBTU, therm, quad) are used primarily in the US for HVAC, natural gas, and national energy statistics.
Atomic-scale units: The electronvolt (eV) and its multiples (keV, MeV) are used in atomic, nuclear, and particle physics for the extremely small energies of individual particles.

Energy in Everyday Life

Nutrition: Food energy is measured in kilocalories (kcal) or kilojoules (kJ). A typical adult needs about 2,000–2,500 kcal (8,400–10,500 kJ) per day.
Electricity: Household electricity consumption is measured in kilowatt-hours (kWh). An average US home uses about 900–1,000 kWh per month.
Heating: Natural gas consumption is measured in therms or MMBTU. A US home might use 500–1,000 therms per year for heating.
Transportation: Gasoline contains about 120,000 BTU or 34 MJ per litre. One gallon of gasoline contains about 33.7 kWh of energy.

Converting Between Energy Units

All energy units measure the same physical quantity, so converting between them is simply a matter of multiplying by the appropriate conversion factor. The factor is the ratio of how many joules one unit of the source contains divided by how many joules one unit of the target contains.

For very large or very small conversion factors, results are often expressed in scientific notation (e.g., 6.2415 × 10¹⁸ eV per joule). This is particularly common when converting between atomic-scale units (electronvolts) and everyday units (joules, BTU, calories).

Tips for Energy Conversions

The joule and watt-second are exactly the same unit (1 J = 1 Ws). The different names are used in different contexts.
For SI metric conversions (J, kJ, MJ, GJ), each prefix step is a factor of 1,000. The same applies to cal/kcal/Mcal, Wh/kWh/MWh, and eV/keV/MeV.
The kilocalorie (kcal) used in nutrition is often written as “Calorie” with a capital C. When a food label says 200 Calories, it means 200 kcal = 200,000 cal.
One kilowatt-hour equals exactly 3,600,000 joules (1 kW × 3,600 seconds). This is useful for converting between electrical and metric energy units.
One BTU ≈ 1,055 joules ≈ 252 calories. These rough equivalences are useful for quick mental conversions.
One therm = 100,000 BTU exactly. One MMBTU = 1,000,000 BTU exactly. One quad = 10¹⁵ BTU exactly.
The electronvolt is an extremely small unit compared to everyday energy: 1 eV ≈ 1.6 × 10⁻¹⁹ J. It is used only for atomic-scale energies.
To calculate electricity cost, multiply kWh × price per kWh. To calculate gas heating cost, multiply therms × price per therm.

Kilojoules to Joules Conversion Table

The following table shows conversions from kilojoules to joules.

Kilojoules	Joules (J)
1 kJ	1,000
2 kJ	2,000
3 kJ	3,000
4 kJ	4,000
5 kJ	5,000
6 kJ	6,000
7 kJ	7,000
8 kJ	8,000
9 kJ	9,000
10 kJ	10,000
11 kJ	11,000
12 kJ	12,000
13 kJ	13,000
14 kJ	14,000
15 kJ	15,000
16 kJ	16,000
17 kJ	17,000
18 kJ	18,000
19 kJ	19,000
20 kJ	20,000
21 kJ	21,000
22 kJ	22,000
23 kJ	23,000
24 kJ	24,000
25 kJ	25,000
26 kJ	26,000
27 kJ	27,000
28 kJ	28,000
29 kJ	29,000
30 kJ	30,000
31 kJ	31,000
32 kJ	32,000
33 kJ	33,000
34 kJ	34,000
35 kJ	35,000
36 kJ	36,000
37 kJ	37,000
38 kJ	38,000
39 kJ	39,000
40 kJ	40,000