Natural Gas Cost Calculator

How to use the natural gas cost calculator

Enter how many therms you used, the price per therm from your gas bill, and, under Advanced, the fixed monthly service charge, and you get back your estimated monthly bill: the total, the energy charge that drives it, and your true all-in cost per therm. All three fields are pre-filled with a representative example — 50 therms at $1.50 a therm with a $12 service charge — so you can watch the tool work before you swap in your own numbers. That $1.50 default is in the right neighbourhood: the Energy Information Administration put the 2025 US residential price of natural gas at $15.34 per thousand cubic feet, which at the US average heat content works out to about $1.48 per therm.

The therms used is the headline usage figure on your gas bill, usually in the usage summary and labelled therms used or therms. It covers the gas that ran your furnace, water heater, stove and dryer over the billing period, so enter that figure exactly rather than estimating it. Winter months run far higher than summer ones because space heating dominates a gas bill — the Energy Information Administration found space heating and air conditioning together accounted for 52 percent of household annual energy use in its 2020 Residential Energy Consumption Survey — so a single month is only a snapshot. To picture a year, run the calculation a few times with high-winter and low-summer usage and see how far the total swings.

The price per therm is the supply rate printed on your bill, not a number to guess at. Natural-gas prices vary widely by region and by season, so always use the dollars per therm from your own statement rather than any national figure, and because this is a gas tool, ignore the cents-per-kWh rate you would use for electricity — different units, different markets. If your bill splits the per-therm charge into a supply rate and a separate delivery rate, add the two per-therm pieces together so the energy charge reflects everything billed by the therm. Some utilities also apply a rider or adjustment per therm, and if yours does, fold that in too.

The fixed monthly service charge lives under Advanced because many people overlook it, but it is on nearly every bill. It is the flat customer charge, basic service charge or service charge the utility bills for keeping you connected at all, regardless of how much gas you burn, so it lands on a low-usage summer bill just as hard as a high-usage winter one. The default of $12 is a fair stand-in, but the real number is printed on your bill. Read the total as your estimated monthly bill, the energy charge as the part that scales with usage, and the all-in cost per therm as what a therm truly costs you once the fixed charge is spread across your usage. That all-in figure is always above the supply rate, and the gap shrinks as you burn more gas.

The formula

A natural-gas bill is two pieces added together: the gas you actually burned, priced by the therm, plus a flat charge for being connected. Multiply your therms by the per-therm rate to get the energy charge, add the fixed service charge, and that sum is the bill. Dividing the total back by the therms gives the number that matters more than either input, the all-in cost per therm — what a therm genuinely costs you once the connection fee is accounted for.

The reason that third figure deserves its own line is that the fixed charge behaves completely differently from the energy charge. One is proportional to usage and one is not, so the blended cost per therm is a curve rather than a constant. It falls as usage rises and climbs steeply as usage approaches zero, which is why a household that heats with gas and cooks with it pays a very different effective price in January and in July even on an identical tariff.

energy charge = therms × rate
total = energy charge + fixed charge
all-in cost per therm = total ÷ therms
therms = ccf × the heat-content factor on your bill, about 1.036

Worked example with the defaults: 50 therms at $1.50 a therm is 50 × $1.50 = $75.00 in energy charges; add the $12.00 fixed service charge and the total is $87.00. Spread that total over the 50 therms and the all-in cost is $87.00 ÷ 50 = $1.74 per therm, 16 percent above the $1.50 supply rate because the fixed charge rides along. Double the usage to 100 therms and the total climbs to $162.00 while the all-in rate falls to $1.62; cut it to 10 therms in July and the total is $27.00 but the all-in rate has ballooned to $2.70.

A therm is a unit of heat energy, defined as exactly 100,000 BTU, which is about 29.31 kWh. Your meter, though, measures volume: ccf, meaning 100 cubic feet of gas. The utility converts one to the other with a heat-content factor, printed on your bill as the therm factor or BTU factor, because a cubic foot of gas does not always carry identical energy. The Energy Information Administration estimated a US average of 1,036 BTU per cubic foot for 2026, which makes a ccf about 1.036 therms. Treating therms and ccf as interchangeable is fine for a rough read and wrong by three or four percent for anything exact.

Two things to keep in mind before you act on the total. First, this is an arithmetic model of a simple two-part tariff, not a bill prediction: many utilities add per-therm riders, seasonal rate blocks, weather normalisation adjustments or state and local taxes that are not represented here, so match the output against a real statement before you trust it. Second, if you are weighing gas heating against an electric heat pump, it is the all-in dollars per therm from this page that should travel into the gas-vs-electric-heating-calculator, since that tool applies furnace AFUE to the gas side and a coefficient of performance to the electric side to put both fuels on the same footing.

Frequently asked questions