What is the unit of heat in the CGS system?

In cgs units, one erg is 1 g cm2 s−2, equal to 1.0×10−7 J.

The imperial/U.S. units for both energy and work include the foot-pound force (1.3558 J), the British thermal unit (Btu) which has various values in the region of 1055 J, and the horsepower-hour (2.6845 MJ).

The energy unit used for everyday electricity, particularly for utility bills, is the kilowatt-hour (kWh), and one kWh is equivalent to 3.6×106 J (3600 kJ or 3.6 MJ). Electricity usage is often given in units of kilowatt-hours per year (kWh/yr). This is actually a measurement of average power consumption, i.e., the average rate at which energy is transferred.

The calorie equals the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J. Food energy is measured in large calories or kilocalories, often simply written capitalized as "Calories" (= 103 calories).

In physics and chemistry, it is still common to measure energy on the atomic scale in the non-SI, but convenient, units electronvolts (eV). The Hartree (the atomic unit of energy) is commonly used in calculations. Historically Rydberg units have been used.

In spectroscopy and related fields it is common to measure energy levels in units of reciprocal centimetres. These units (cm−1) are strictly speaking not energy units but units proportional to energies, with hc being the proportionality constant.