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 watt-hour (Wh) equals 3,600 joules, representing the energy consumed by a one-watt device operating for one hour. It is commonly used for small battery capacities, solar panel output ratings, and electric vehicle charging metrics where kilowatt-hours would be too large a unit. One watt-hour equals exactly 0.001 kilowatt-hours or about 3.412 BTU.