How is "heat" primarily measured?

Heat is primarily measured in joules, which is the standard unit of measurement for energy in the International System of Units (SI). A joule quantifies the amount of energy transferred when a force of one newton is applied over a distance of one meter. This makes it a versatile unit for measuring thermal energy, as it represents the energy transfer associated with heat.

While other units listed, such as degrees, kilowatts, and watts, relate to heat in various contexts, they do not measure the thermal energy itself. Degrees are used to describe temperature, which indicates the thermal state of a substance but does not equate directly to the amount of heat energy. Kilowatts and watts measure power, which is the rate of energy transfer; these units express how much energy is used over time rather than the total amount of heat energy present. Thus, the measurement of heat itself is most accurately expressed in joules.