Joules and calories both measure energy. The word "calorie" has at least two different definitions, making the term too ambiguous for most scientific work. Because of this, the scientific community adopted the standard unit of joule.
Joules
The term joule, named for the English physicist James Joule, defines a specific measurement of work, in force per unit area. The definition of 1 joule equals the work accomplished by the force of 1 newton acting through a distance of 1 meter. Joule also refers to the work done when passing a current of 1 ampere through a resistance of 1 ohm for one second, according to the Merriam-Webster online dictionary.
Calorie
The term "calorie" can refer to a kilocalorie, an international calorie or a thermocalorie. A kilocalorie describes the amount of energy in foods, often called the "dieter's calorie," or Calorie (note the capital "C"). Scientifically, 1 calorie equals the amount of heat necessary to raise the temperature of 1 gram of water 1 degree Celsius at a pressure of 1 atmosphere, sometimes referred to as the gram-calorie, or calorie with a lowercase "c," the Sizes website explains. A kilocalorie equals 1,000 gram-calories.
Conversion
By definition, the thermochemical calorie, defined by the U.S. Bureau of Standards in 1953, equals exactly 4.1840 joules. Therefore, 677 calories equals 2832.568 joules.
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