The
metric unit of
heat energy is the
calorie (heat can also be measured in
joules, the metric unit of energy in general). It's the amount of energy that must be input (i.e., turned into
entropy) to raise the
temperature of one
gram of
water by one
degree Celsius.
It has achieved fame as the measure of energy derivable when an animal eats a given amount and type of
food.
I once looked at a British candy bar wrapper, and my eyes bugged out. 300 kilocalories??? Then I remembered.
When "Calorie" is capitalized, it refers to one
metric kilocalorie, the amount of energy needed to rase one
kilogram of water by one degree Celsius, or one gram of water by one thousand degrees Celsius, which doesn't actually happen.
American nutritional labels use Calories, regardless of whether the designer remembered to capitalize it. Trust me.