How this calculator works
CCF is a gas-billing volume equal to one hundred cubic feet. A therm is an energy unit equal to 100,000 British thermal units. The two only connect through the heat content of the gas: one cubic foot of natural gas usually releases about 1,000 to 1,050 Btu when burned. At the United States average of about 1,037 Btu/ft³, one CCF holds about 103,700 Btu, or 1.037 therms. A utility that bills one CCF as exactly one therm is using a rounded 1,000 Btu/ft³, so check the heat content printed on your bill.
Formula
Btu = CCF x 100 ft³/CCF x heat content (Btu/ft³). Therms = Btu / 100,000 = CCF x heat content / 1,000. CCF = therms x 1,000 / heat content. GJ = Btu x 1,055.05585262 / 10^9.
Worked example
1 CCF at 1,037 Btu/ft³ is 103,700 Btu, or 1.037 therms. 10 CCF is 10.37 therms. 20 therms at 1,000 Btu/ft³ is 20 CCF; at 1,037 Btu/ft³ it is 19.286 CCF.
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Frequently asked questions
Is one CCF always one therm?
No. It is one therm only when the gas contains exactly 1,000 Btu per cubic foot. Real natural gas varies with its source, so many utilities apply a heat-content factor and bill slightly more or less than one therm per CCF.
Why does my bill use both CCF and therms?
The meter measures volume in CCF, while the rate is often set per unit of energy in therms. The utility measures or estimates the heat content to translate one into the other.
What is a therm in joules?
One therm is 100,000 International Table Btu, which is about 105.506 megajoules or 29.307 kilowatt-hours.