What is the metric unit of heat measurement?

The metric unit of heat measurement is the joule. The joule is the standard unit of energy in the International System of Units (SI), which also encompasses the metric system. One joule is defined as the amount of energy transferred when one newton of force is applied over one meter.

In the context of heat, the joule quantifies energy transfer and is used in various calculations involving thermodynamics. Although the calorie is another unit of heat measurement, it's not a pure metric unit as it is more commonly used in food energy contexts and isn't integrated into the SI system as thoroughly as the joule is. Other options like Fahrenheit and Btu (British thermal unit) are units of temperature and heat, respectively, but they do not represent metric units. Thus, the joule is the correct choice as it reflects the accepted metric standard for measuring heat energy.