The meter measures one thing and the rate charges for another
A residential gas meter counts volume. It advances in cubic feet, and the bill usually reports that volume in CCF, meaning one hundred cubic feet, or in MCF, meaning one thousand. But gas is sold as energy, because a cubic foot of gas does not always carry the same amount of heat. The unit of energy is the therm, defined as exactly 100,000 BTU, and the bridge between volume and energy is a factor the utility publishes on the bill.
That factor is close to 1.03 for most pipeline gas, meaning a hundred cubic feet carries a little over one therm of heat. So 100 cubic feet at a factor of 1.03 is 1.03 therms. It is not a constant. Utilities recalculate it periodically from the composition of the gas actually delivered, and it differs between utilities and across seasons. The number is on your bill, usually near the usage figures and often labelled BTU factor or therm factor, and using yours instead of a nominal 1.0 is the difference between an estimate that lands and one that is quietly three percent light every month.
| Unit | Volume | Therms at a 1.03 factor |
|---|---|---|
| 1 CCF | 100 cubic feet | 1.03 |
| 1 MCF | 1,000 cubic feet | 10.3 |
| 1 therm | about 97 cubic feet | 1.00, by definition 100,000 BTU |
| 1 MMBtu | about 971 cubic feet | 10.00 |
Supply and delivery are two different businesses on one bill
The supply or commodity charge is the cost of the gas molecules. On a regulated utility this is typically passed through at cost with no markup, reset on a schedule that is often monthly, and it is the part that moves when wholesale gas markets move. If you have signed up with a third-party supplier, this is the line their rate applies to and the only line they affect.
The delivery or distribution charge pays for the pipes, the meter, the crews and the utility itself. It is charged per therm on most residential tariffs, sometimes with a declining block structure at higher usage, and it does not fall when gas prices fall. On many bills it is comparable in size to the supply charge, which is why an estimate built from a headline gas price alone comes out far too low. Both rates go into this calculator separately so the split is visible.
Then there is the customer charge, a flat monthly amount for being connected. It is the reason a July bill in a house with gas hot water and nothing else can still be double digits, and the reason the cost per therm looks terrible in summer and reasonable in January.
Reading a meter and understanding the period
Most residential gas meters have a row of dials or a digital display reading in hundreds of cubic feet, so the difference between two readings is CCF directly. Adjacent dials rotate in opposite directions, and the rule for the dial type is to read the number the pointer has passed, not the nearest one. Take readings at the same time of day and the difference is clean.
Billing periods are read-to-read and vary by several days, which matters more for gas than for almost anything else because usage is so seasonal. A 34-day period spanning a cold snap against a 28-day period in a mild stretch is not a comparison of anything. Normalise by dividing therms by days before deciding whether usage moved, and expect winter and summer to differ by a factor of five or more in a house heated by gas.
Where heating goes, and what changes it
In a house with gas heat, space heating dominates the winter bill and hot water dominates the summer one, with cooking a small remainder. That shape is worth knowing because it tells you which changes are worth making at which time of year. A thermostat setback affects the winter number and does nothing in July. A shorter shower or a lower water heater setting affects both, but the effect is only visible in summer when nothing else is running.
The changes that reliably reduce therms are the dull ones: sealing air leaks around windows, doors, rim joists and penetrations; insulating where insulation is thin; letting the thermostat fall while the house is empty or asleep; and servicing the furnace so it burns as designed. A degree of setback is worth something like a percent or two of heating energy over a long period, but that figure depends on the building and the climate far more than on any table, and the only reliable measurement is your own therms per day across comparable weather.
When the reconstruction does not match
Enter what the bill actually came to and this page will back out your true cost per therm. If the two are more than a few percent apart, look first at whether you are on budget billing, which charges a levelled monthly amount and settles up later, so the bill has almost nothing to do with the month it covers. Then check whether the delivery rate is tiered rather than flat, whether a weather-normalisation adjustment appears, and whether the supply rate changed inside the period. Once you have the true all-in figure, that is the number to carry into any decision about insulation, a thermostat or an appliance, and this page has done its job.
Questions people ask
How many therms are in a CCF?
A little over one, and the exact figure is on your bill. One CCF is 100 cubic feet of gas; a therm is 100,000 BTU of energy. The utility multiplies the volume by a heat-content factor to convert, and that factor is commonly around 1.03, so 100 cubic feet works out to roughly 1.03 therms. It is not fixed: it depends on the composition of the gas being delivered and is recalculated periodically, so it differs between utilities and can shift between seasons. Look for a line called BTU factor, therm factor or heat content near the usage figures.
What is the difference between a therm and an MCF?
A therm is a unit of energy equal to 100,000 BTU. An MCF is a unit of volume equal to 1,000 cubic feet, which is ten CCF. At a heat-content factor of 1.03 an MCF carries about 10.3 therms. Residential bills usually use therms or CCF; MCF turns up on commercial accounts and in wholesale market quotes, alongside MMBtu, which is a million BTU and therefore exactly ten therms. If you are comparing a price you saw quoted per MMBtu against your own bill, divide it by ten to get a per-therm figure, and remember that the quoted market price is supply only and carries none of your delivery charges.
Why did my gas bill go up when I did not change the thermostat?
Check four things in order. The number of days in the period, since read-to-read cycles vary and a longer period is more of everything. Therms per day rather than therms per bill, which removes that effect. The weather, because heating energy tracks how cold it was far more closely than anything you did indoors, and a stretch of unusually cold days moves usage a long way. And the supply rate, which on many utilities is reset monthly and passed straight through, so identical usage can cost noticeably more or less than last month with nothing changed at your end.
Is the delivery charge negotiable if I switch suppliers?
No. A third-party supplier can only change the supply or commodity portion of the bill, which is the cost of the gas itself. The delivery charge, the customer charge and the taxes stay with your local utility regardless of who supplies the gas, because the utility still owns the pipes and reads the meter. That matters when comparing offers: a supply rate that undercuts the utility default by a large percentage moves a smaller share of the total bill than the percentage suggests, and introductory rates that convert to variable pricing after a few months are the usual place people lose the saving.