SafekipediaCalorie
Adapted from Wikipedia · Adventurer experience
The calorie is a unit of energy that comes from old ideas about heat. It tells us how much energy is in food and how our bodies use that energy.
In everyday life, the word “calorie” usually means a larger amount of energy called a kilocalorie. This is why food labels show calories — they tell us how much energy we get from eating.
In science, the calorie is not the main unit we use anymore. Scientists now prefer to use the joule, which is the standard unit of energy. But the calorie is still very important in nutrition and food science. It helps us understand how much energy different foods give us and how much our bodies need to stay healthy.
History
The word "calorie" comes from a Latin word meaning 'heat'. It was first used to measure heat energy by a scientist named Nicolas Clément in the early 1800s.
Later, scientists began using the same word for a smaller amount of heat energy.
Some people started using a big "C" to show the larger amount of heat, called a kilocalorie. This helped avoid confusion between the two sizes of calories.
Today, scientists mainly use a unit called the joule to measure energy, but the calorie is still sometimes used, especially when talking about food energy.
Definitions
The "small" calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. This definition can change a little depending on the air pressure and starting temperature of the water.
Before 1948, scientists used a value of 4.1833 international joules for this measurement. Today, the standard is 4.184 J, which keeps the meaning the same as before.
| Name | Symbol | Conversions | Definition and notes |
|---|---|---|---|
| Thermochemical calorie | calth | ≡ 4.184 J | The amount of energy equal to exactly 4.184 J (joules) and 1 kJ ≈ 0.239 kcal. |
| 4 °C calorie | cal4 | ≈ 4.204 J ≈ 0.003985 BTU ≈ 1.168×10−6 kWh ≈ 2.624×1019 eV | The amount of energy required to warm one gram of air-free water from 3.5 to 4.5 °C at standard atmospheric pressure. |
| 15 °C calorie | cal15 | ≈ 4.1855 J ≈ 0.0039671 BTU ≈ 1.1626×10−6 kWh ≈ 2.6124×1019 eV | The amount of energy required to warm one gram of air-free water from 14.5 to 15.5 °C at standard atmospheric pressure. Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J. |
| 20 °C calorie | cal20 | ≈ 4.182 J ≈ 0.003964 BTU ≈ 1.162×10−6 kWh ≈ 2.610×1019 eV | The amount of energy required to warm one gram of air-free water from 19.5 to 20.5 °C at standard atmospheric pressure. |
| Mean calorie | calmean | ≈ 4.190 J ≈ 0.003971 BTU ≈ 1.164×10−6 kWh ≈ 2.615×1019 eV | Defined as 1⁄100 of the amount of energy required to warm one gram of air-free water from 0 to 100 °C at standard atmospheric pressure. |
| International Steam Table calorie (1929) | ≈ 4.1860 J ≈ 0.0039683 BTU ≈ 1.1630×10−6 kWh ≈ 2.6132×1019 eV | Defined as 1⁄860 "international" watt hours = 180⁄43 "international" joules exactly. | |
| International Steam Table calorie (1956) | calIT | ≡ 4.1868 J ≈ 0.0039683 BTU = 1.1630×10−6 kWh ≈ 2.6132×1019 eV | Defined as 1.163 mWh = 4.1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956). |
Usage
In North America, people use a unit called the calorie, written with a lowercase "c" and the symbol "cal", to talk about food and nutrition. Sometimes, scientists use a different unit called the kilojoule (kJ). Most American experts use kilocalories, while many scientists use kilojoules. In other countries, experts usually use kilojoules.
In Europe, food labels show energy in both kilojoules and kilocalories, written as "kJ" and "kcal". In China, only kilojoules are used.
This unit helps us talk about the energy in food. For example, fats have 9 kilocalories per gram, while carbohydrates and proteins have about 4 kilocalories per gram. Alcohol in food has 7 kilocalories per gram. The calorie is also used to talk about how many calories people should eat each day.
Eating in a controlled way can help body weight and prevent or treat diseases like diabetes and obesity.
In chemistry and physics, the term "calorie" can mean a smaller unit, with the large unit called a kilocalorie (kcal). It is used to measure energy in chemical reactions. However, the joule (J) and its multiples, like the kilojoule (kJ), are now used more often.
Related articles
This article is a child-friendly adaptation of the Wikipedia article on Calorie, available under CC BY-SA 4.0.
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