One calorie is the energy required to raise the temperature of one gram of water at 1 atm pressure by one degree Celsius, it is equal to about 4.2 Joules. A kil

One calorie is the energy required to raise the temperature of one gram of water at 1 atm pressure by one degree Celsius, it is equal to about 4.2 Joules. A kilocalorie, or a dietary Calorie, is one thousand calories, or 4200 Joules. All of this is readily available from an innumerable number of sources. The calorie content of food is determined experimentally by burning the food in a calorimeter and measuring how much heat is produced (by, for example, measuring how much it raises the temperature of a water bath). This measures the energy content of the food, but does not measure the amount of energy your body can make use of as that is a very complex problem that would have a different answer in every individual due to variations in body size, metabolism, digestion, muscle mass, insulin activity, the ambient temperature, and about a zillion other factors.