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 kilowatt-hour (kWh) equals 3,600,000 joules and is the standard billing unit for residential and commercial electricity consumption worldwide. Utility companies charge by the kilowatt-hour, and understanding this unit helps consumers evaluate appliance running costs and solar panel output. One kilowatt-hour represents the energy used by a 1,000-watt appliance running for one hour.