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The calorie is a unit of energy that originated from the caloric theory of heat. [ 1 ] [ 2 ] The large calorie , food calorie , dietary calorie , or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter of water by one degree Celsius (or one kelvin ).
For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J. In many regions, food energy is measured in large calories (a large calory is a kilocalory, equal to 1000 calories), sometimes written capitalized as Calories. In the European Union, food energy ...
Some organisms have instead anaerobic respiration, which extracts energy from food by reactions that do not require oxygen. The energy contents of a given mass of food is usually expressed in the metric (SI) unit of energy, the joule (J), and its multiple the kilojoule (kJ); or in the traditional unit of heat energy, the calorie (cal).
Because food energy is commonly measured in Calories, the energy density of food is commonly called "caloric density". [7] In the metric system, the energy unit commonly used on food labels is the kilojoule (kJ) or megajoule (MJ).
The number of calories you need to cut to shed pounds depends on your weight, daily calorie burn, hormones, and more. However, a good rule of thumb: Eating 500 fewer calories per day will help you ...
The British thermal unit (Btu) is a measure ... The thermochemical calorie is exactly 4 ... An early effort to define heat units directly in terms of energy units ...
In chemistry, heat amounts were often measured in calories. Confusingly, there are two common units with that name, respectively denoted cal and Cal: the small calorie (gram-calorie, cal) is 4.184 J exactly. It was originally defined so that the specific heat capacity of liquid water would be 1 cal/(°C⋅g).
However energy can also be expressed in many other units not part of the SI, such as ergs, calories, British thermal units, kilowatt-hours and kilocalories, which require a conversion factor when expressed in SI units. The SI unit of power, defined as energy per unit of time, is the watt, which is a joule per second. Thus, one joule is one watt ...