How to use this calculator
Enter your natural gas usage in CCF (hundred cubic feet) — you'll find this figure on your gas utility bill. Then enter the heating value factor, which defaults to 1.037 therms per CCF, the industry-standard approximation. Click Calculate to see your usage converted to therms, the unit most gas utilities actually bill you for.
What is a CCF and what is a therm?
CCF stands for "centum cubic feet," using the Roman numeral prefix "C" for hundred, so 1 CCF equals 100 cubic feet of natural gas. It is a volume measurement. A therm, by contrast, is a unit of heat energy equal to 100,000 British Thermal Units (BTU). Utilities bill customers in therms (or sometimes dekatherms, equal to 10 therms) because energy content, not raw volume, is what actually determines how much gas is worth and how much heat it can produce.
The conversion formula
Therms = CCF × heating value factor. Natural gas is not perfectly uniform — its energy content varies slightly by source and moisture content, averaging close to 1,037 BTU per cubic foot in the United States. Since 1 CCF = 100 cubic feet, that works out to about 100 x 1,037 = 103,700 BTU per CCF, and since 1 therm = 100,000 BTU, dividing gives 103,700 / 100,000 = 1.037 therms per CCF. This 1.037 factor is the conversion multiplier most U.S. utilities use, though your specific utility publishes its own monthly factor (typically between about 1.00 and 1.05) on your bill because gas heating content fluctuates slightly with supply source and season.
Why utilities don't just charge for cubic feet
Two CCF of gas from different pipelines can contain slightly different amounts of usable energy depending on the gas mixture. Billing in therms (an energy unit) rather than CCF (a volume unit) ensures customers pay for the heat they actually receive, not just the space the gas occupied. This is the same reason electricity is billed in kilowatt-hours (energy) rather than amperes (current) alone.
Reference values worth knowing
- 1 CCF = 100 cubic feet of natural gas
- 1 therm = 100,000 BTU = 29.3 kilowatt-hours
- 1 CCF ≈ 1.037 therms (typical U.S. average heating value)
- 1 dekatherm (Dth) = 10 therms
- A typical U.S. household uses roughly 3 to 10 CCF per month in summer and 15 to 30+ CCF per month in winter for heating, though this varies enormously by climate and home size.
Worked example
If your meter shows you used 65 CCF this month and your utility's published heating factor is 1.037, your billed energy usage is 65 × 1.037 = 67.4 therms. If your gas rate is, for example, $1.20 per therm, your gas charge (before delivery fees and taxes) would be about 67.4 × $1.20 = $80.90.
FAQ
Why isn't the factor always exactly 1.037? The heating value of natural gas depends on its exact composition (mostly methane, with small amounts of ethane, propane, and other gases), which varies by supplier and over time. Utilities publish an updated factor — sometimes called the "BTU factor" or "thermal conversion factor" — on each bill, and it commonly ranges from about 1.00 to 1.05.
Where do I find my CCF usage? It is printed on your gas bill, usually next to your meter readings, or you can read it directly from your gas meter if it displays cubic feet.
Is a CCF the same as an MCF? No. MCF traditionally refers to 1,000 cubic feet (using the Roman numeral "M" for thousand), so 1 MCF = 10 CCF. Don't confuse the two when comparing bills or industry data.
How do therms relate to kilowatt-hours? 1 therm equals approximately 29.3 kWh of energy, which is useful when comparing gas heating costs to electric heating costs.
Does this calculator account for delivery charges or taxes? No — it only converts CCF volume to therms of energy. Your total bill also includes delivery/distribution charges, taxes, and sometimes a fixed customer charge, which vary by utility and are not part of this unit conversion.