The kilocalorie (kcal), commonly called the 'Calorie' on food labels, equals 1,000 calories or 4,184 joules, the standard unit for measuring dietary energy worldwide. When nutrition facts list '200 Calories,' they mean 200 kilocalories, representing the energy your body can extract from that food. One kilocalorie equals exactly 4.184 kilojoules, the figure used on food packaging in many countries.

The BTU (British Thermal Unit) equals approximately 1,055.06 joules, defined as the heat needed to raise one pound of water by one degree Fahrenheit. It is the primary unit for rating heating and cooling equipment in the United States, appearing on air conditioner specifications, furnace ratings, and energy efficiency labels. One BTU equals about 0.2931 watt-hours or roughly 0.252 kilocalories.