kJ

Kilojoule (symbol kJ) is the unit of energy in the International System of Units (SI). It equals 1,000 joules, with the joule defined as the work done when a force of one newton acts over a distance of one meter. As an SI unit, the kilojoule is used to express energy, heat, and work in physics, chemistry, engineering, and related fields.

In scientific contexts, energy changes and amounts are frequently given in kilojoules or in kilojoules per mole (kJ/mol) to reflect the quantity of substances involved. The kilojoule is also used to quantify electrical energy and thermal energy transfer, such as heating or cooling processes, where larger values are convenient to report than joules.

In nutrition, energy content of foods is commonly reported in kilojoules and kilocalories (food calories). One kilocalorie equals 4.184 kilojoules, so one kilojoule is approximately 0.239 kilocalories. This dual convention means energy on nutrition labels can be presented in either unit, depending on the region. Other common conversions include: 1 kJ ≈ 0.9478 BTU, 1 kJ ≈ 0.2778 watt-hours (Wh), and 1 kJ ≈ 0.0002778 kilowatt-hours (kWh).

The kilojoule is widely used because it aligns with the joule while providing a convenient magnitude for everyday energy scales. It coexists with related units such as the calorie, joule, and watt-hour in various applications, standards, and labeling requirements.