A calorie is an unit of measurement for energy.
The calorie was never a metric or SI unit.
In most fields, it has been replaced by the joule, the SI unit of energy.
It remains, however, in common use for the amount of energy obtained from food.
Recommended daily energy intake values for young adults are: 2500 kcal/d for men and 2000 kcal/d for women.
Nutritional calories are not measured amounts of energy, but are calculated from food composition.
Such calculations use internationally agreed conventional conversion factors, which are generously rounded values that roughly approximate the average energy density of a large number of different food samples.