How is heat energy measured?

Heat energy is measured in joules, calories, and BTUs because these units are specifically designed to quantify thermal energy.

Joules are the standard unit of energy in the International System of Units (SI), and they are used for various forms of energy, including heat. Calories are traditionally used to measure heat energy, particularly in the context of food and nutrition, where it describes the amount of energy that food provides. BTUs, or British Thermal Units, measure heat energy as well, particularly in the heating and cooling industries, indicating the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

The other measurement units, such as liters, grams, and square meters, do not measure heat energy. Liters measure volume, grams measure mass, and square meters measure area, none of which directly pertain to the measurement of thermal energy. Thus, the correct choice emphasizes the recognized units specifically associated with heat energy.