Kilocalorie (kcal)
The kilocalorie, symbolized as kcal, equals 1,000 calories and is often referred to as a “Calorie” with a capital C in food labeling. It measures the energy in food and human metabolism, helping dieticians, nutritionists, and consumers track intake. The kilocalorie became the standard unit of energy measurement as nutrition science linked energy measurement to diet. Most scientists now use joules, but kilocalories are still commonly used in reporting food energy.
Watt Hour (Wh)
The watt-hour, symbolized as Wh, represents the energy consumed when one watt of power is used for one hour, equivalent to 3,600 joules. Introduced with the spread of electrical systems in the late 19th century, the watt-hour is a practical unit for measuring smaller-scale electrical consumption, such as that of batteries and small devices. It is widely used in electronics, computing, and renewable energy storage. While large-scale power use is measured in kilowatt hours, watt-hours provide fine-grained detail for portable and household applications.