What is kilojoule?

A kilojoule is a unit of energy equal to 1,000 joules. It is commonly used in nutrition to express the energy content of food, as well as in thermodynamics and mechanical engineering.

Real-world uses

Kilojoules are the standard energy unit for food nutrition labelling in Australia, New Zealand, and parts of Europe (alongside kilocalories). A typical adult daily intake is about 8,700 kJ. They are also used in chemistry for reaction enthalpies and combustion energies.

History

The kilojoule became important in nutrition labelling as countries adopted SI-based energy reporting. Australia was among the first to mandate kJ on food labels in the 1970s. The EU requires both kJ and kcal on nutrition labels.

Common mistakes

Confusing kilojoules with kilocalories—1 kcal = 4.184 kJ. Food labels showing "2000 kJ" are about 478 kcal, not 2000 kcal. Also, some people incorrectly assume kJ and kW are the same thing; one is energy, the other is power.

What is therm (US)?

A US therm is a unit of energy equal to 100,000 BTU. It is used by gas utility companies in the United States as the standard billing unit for natural gas consumption.

Real-world uses

The therm is used in the United States and United Kingdom for natural gas billing. One therm equals 100,000 BTU (approximately 29.3 kWh). Residential gas bills in the US often list consumption in therms. It is also used in industrial gas metering and procurement contracts.

History

The therm was introduced as a practical unit for natural gas billing in the early 20th century, when gas supply companies needed a convenient large-scale energy unit for residential and commercial customers. It consolidated prior inconsistent measurement practices in the gas industry.

Common mistakes

Confusing the therm with the BTU—1 therm = 100,000 BTU. Also, the US therm and the UK therm differ slightly (the UK therm is based on 105.5 MJ, while the US therm is exactly 100,000 BTU ≈ 105.48 MJ). Not to be confused with the thermie (a metric unit of heat).

When is this conversion used?

Converting between kilojoule and therm (US) is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Nutritional information is labelled in kilocalories in some countries and kilojoules in others, making this conversion important for dietary planning and food science.

Worked examples

1 kilojoule = 0.00000948 therm (US)

1 therm (US) = 105,506,000 joule

How to convert kilojoule to therm (US)

To convert kilojoule to therm (US), multiply the value by 0.00000948.

To convert therm (US) back to kilojoule, multiply by 105,506.

Measurement standards

The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.

Did you know?

A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.

Quick reference: kilojoule to therm (US)

kilojoule	therm (US)
0.1	9.478134e-07
0.5	0.00000474
1	0.00000948
2	0.00001896
5	0.00004739
10	0.00009478
25	0.00023695
50	0.00047391
100	0.00094781
250	0.00236953
500	0.00473907
1,000	0.00947813

Common values

	kilojoule	therm (US)
A food calorie (1 kcal)	4.184 kilojoule	0.00003966 therm (US)
A AA battery	9.36 kilojoule	0.00008872 therm (US)
Boiling a kettle	420 kilojoule	0.00398082 therm (US)
Daily human diet (2000 kcal)	8,368 kilojoule	0.07931302 therm (US)
1 gallon of gasoline	131,760 kilojoule	1.24883893 therm (US)

Available Energy units

More kilojoule conversions

Assumption: calorie means thermochemical calorie, and therm means US therm.