Why natural gas conversion needs an assumption
Volume units such as cubic feet and cubic metres measure how much gas occupies a space. Energy units such as therms, MMBtu, and kWh measure the heat energy available from that gas. To move between the two, the converter needs a typical heat-content assumption.
That heat content varies slightly with gas composition and delivery conditions. A consumer-facing converter therefore uses common average relationships so you can compare units quickly, while a utility bill or industrial contract may apply a local factor that differs a little from the generic result.
1 Mcf = 1,000 ft³
Mcf is a thousand-cubic-foot volume unit commonly used in pricing and reporting.
1 therm = 100,000 Btu
Therm is a standard consumer billing-energy unit in many natural gas markets.
1 kWh = 3,412 Btu
Kilowatt-hours let you compare gas energy with electricity on the same broad basis.