Natural gas utilities bill in either therms (units of energy) or CCF (units of volume, equal to roughly 1.025 therms). The two units measure different things and the conversion depends on the heating value of the gas in your region. Most US utilities standardized on one unit or the other based on regulatory history and have stayed there for decades. Here is the unit difference, the conversion factor, and how to read either format on your bill.
Definitions: therm, CCF, dekatherm
A therm is 100,000 BTU of energy. It is a unit of heat content, not volume. Most US utilities in PA, OH, IL, NJ, and MD bill in therms.
A CCF (centum cubic feet) is 100 cubic feet of gas volume. The energy content depends on heating value — typically 1,020 to 1,040 BTU per cubic foot — which means 1 CCF equals roughly 1.020 to 1.040 therms. California utilities and some southwestern utilities bill in CCF.
How to convert between therms and CCF
The conversion factor is your utility's published heating value, sometimes called the BTU factor. Find it on the bill (usually near the usage section).
Most US heating values run between 1.020 and 1.040 BTU per cubic foot. For quick estimation, multiply CCF by 1.03 to get therms. Multiply therms by 0.97 to get CCF.
Which unit does your utility use?
Look on your bill for the usage line. The unit will be labeled THERMS, CCF, MCF (1,000 cubic feet), or DT/Dth (dekatherms). Therms and CCF are most common for residential.
Industrial customers often see MMBtu (million BTU) or Dth (dekatherm). Both are bigger units appropriate for commercial volumes. 1 MMBtu equals 10 therms equals 1 dekatherm.
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