therm

A therm is a unit of heat energy used primarily in the United States and Canada to measure the energy content of natural gas. It is not an SI unit. The therm is defined as 100,000 British thermal units (BTU).

Since 1 BTU is approximately 1,055 joules, 1 therm equals about 105,500,000 joules (105.5 megajoules). In electrical terms, with 1 kilowatt-hour equal to 3.6 megajoules, 1 therm is roughly 29.3 kilowatt-hours.

Gas utilities commonly bill by therms, reflecting energy content rather than volume because the calorific value of natural gas varies with composition and temperature. To convert gas volume to therms, standard conditions are used. The therm is often discussed alongside the dekatherm (DTh), where 1 DTh equals 1,000,000 BTU or 10 therms.

Origin and usage: The term originated in the gas industry as a practical energy unit. It remains common in North American natural gas markets for billing and energy accounting, though SI units such as joules or watt-hours are used in other contexts and international reporting.