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.

The therms used is the headline usage figure on your gas bill, usually in the usage summary and labelled “therms used” or “therms.” It is the gas that ran your furnace, water heater, stove, and dryer over the billing period. Enter that figure exactly. Winter months run far higher than summer ones because space heating dominates a gas bill, 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 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 season, so always use the $/therm from your own gas bill rather than any national figure — and because this is a gas tool, ignore the ¢/kWh rate you would use for electricity; they are different units and 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.

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 you for being 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; enter it and the total will match what you actually pay.

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 a little higher than the supply rate, and the gap shrinks as you use more gas, because the fixed charge is divided over more therms. If you want to weigh gas heating against an electric heat pump or resistance heat, the all-in $/therm here is the right number to carry into the gas-vs-electric-heating-calculator, which puts the two fuels on the same footing.

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:

energy charge = therms × rate
total = energy charge + fixed charge

Worked example with the defaults — 50 therms at $1.50 a therm: 50 × $1.50 = $75.00 energy charge; add the $12.00 fixed service charge and the total is $87.00. Spread that total over the 50 therms and your all-in cost is $87.00 ÷ 50 = $1.74 per therm — higher than 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 drifts down toward the supply rate as the $12 spreads thinner.

A therm is a unit of heat energy: one therm equals 100,000 BTU, which is about 29.3 kWh of energy — so a therm is a sizeable chunk of fuel. Your meter, though, usually measures CCF — 100 cubic feet of gas — and the utility multiplies each CCF by a heat-content factor (the “therm factor,” typically about 1.0 to 1.04) to convert volume into therms, since not every cubic foot carries identical energy. For a quick read therms ≈ CCF, but for an exact bill check your bill’s printed therm factor and apply it.

Frequently asked questions