A therm measures energy. Your meter measures volume. Those are not the same thing.
Your gas meter spins as cubic feet of gas flow through it. But a cubic foot of cold, dense gas at 5 a.m. in January contains more energy than the same cubic foot of warm, expanded gas at 3 p.m. in July. If utilities billed by volume alone, you would pay different prices for the same heat depending on the season.
So utilities bill by energy, not volume. Specifically, they bill in therms. One therm is exactly 100,000 BTU, the energy needed to heat 1,000 pounds of water by 100 degrees Fahrenheit.
Every month your utility multiplies the volume you used (in CCF or Mcf) by a small monthly BTU correction factor printed on your bill. That converts volume to therms. The therms times the per-therm rate is your supply charge.
Therm, BTU, kWh, CCF, Mcf — what each one is.
US energy uses three energy units (BTU, therm, kWh) and two volume units (CCF, Mcf). Once you know which is which, the conversions become obvious.
Energy units
BTU · therm · kWh
These measure energy delivered, regardless of fuel or temperature. 1 BTU is tiny; 1 therm is 100,000 BTU; 1 kWh is about 3,412 BTU.
Volume units
CCF & Mcf
These measure cubic feet of gas. CCF is 100 cubic feet, Mcf is 1,000. Your meter reads in one of these. Volume alone does not tell you energy.
The bridge
BTU correction factor
A monthly multiplier (typically 1.00 to 1.05) that converts your meter's volume reading into therms. Set by your utility, printed on your bill.
Energy units (BTU, therm, kWh) are interchangeable through fixed factors. Volume units (CCF, Mcf) need the monthly correction factor to become energy units.
Every conversion you will ever need.
Memorize one row and you can derive the rest. The therm is the natural pivot because it ties gas volume and electric energy together cleanly.
| From | Equals | In BTU | In kWh |
|---|---|---|---|
| 1 therm | 100,000 BTU | 100,000 | 29.3 |
| 1 kWh | 3,412 BTU | 3,412 | 1.000 |
| 1 CCF (100 ft³) | ~1.025 therms | 102,500 | 30.0 |
| 1 Mcf (1,000 ft³) | ~10.37 therms | 1,037,000 | 303.9 |
| 1 dekatherm | 10 therms | 1,000,000 | 293.0 |
| 1 MMBTU | 10 therms | 1,000,000 | 293.0 |
In wholesale markets gas trades in MMBTU (Henry Hub futures) or dekatherms. Both equal 10 residential therms. Utilities then resell to you in therms.
Per unit of energy, US gas is 3.6x cheaper than electricity.
A therm of gas delivers 29.3 kWh of energy and costs about $1.45 at US average prices. The same 29.3 kWh of electricity at the wall costs about $5.25.
That ratio is why ~58% of US homes still heat with natural gas (EIA 2023 Residential Energy Consumption Survey). It also explains why utilities push electrification carefully: the raw fuel arithmetic favors gas by a wide margin.
But raw fuel cost is not the whole story. The next section is where most comparisons go wrong.
same amount of energy, two ways to buy it
Efficiency is what turns the gas advantage on its head.
Burning fuel and moving heat are not the same thing. A heat pump does not generate heat at all; it moves heat from outside into your house. That changes the math completely.
Gas furnace: 80–98% efficient
A modern condensing furnace delivers about 95% of the therm as useful heat. A 30-year-old furnace might run at 80%. Anything below 80% is now banned for new installs under DOE rules.
Electric resistance: exactly 100%
Baseboards and resistance furnaces turn every kWh into 1 kWh of heat. No more, no less. At US average rates this is almost always the most expensive way to heat.
Heat pump: 200–400% effective (COP 2–4)
A heat pump uses 1 kWh of electricity to move 2–4 kWh of heat. At a COP of 3, that 17.91¢/kWh becomes effectively 5.97¢ per delivered kWh — competitive with gas.
The crossover
In states with cheap electricity (ND, WA, NE at 11–12¢/kWh), a heat pump at COP 3 already beats a 95% gas furnace on operating cost. In high-rate states (CA, HI, MA), a heat pump needs COP 4+ to break even.
This is why "gas is cheaper" is a 2010-era answer. With modern cold-climate heat pumps now hitting COP 2+ at 5°F, the comparison is no longer one-sided. Always compare cost per delivered kWh of heat, not per unit of fuel purchased.
How US households get the math wrong.
Five recurring errors we see when readers compare gas to electricity. Each one quietly steers a household to the wrong heating system.
How many therms does a US household actually use?
A typical US home that heats with natural gas uses 70–90 therms per month on average over the year, but the distribution is heavily seasonal. Winter peaks easily hit 150–200 therms; summer months can drop to 5–15 therms (water heater and stove only).
That averages out to roughly 900 therms per year — about $1,300 at $1.45/therm — for heating, hot water and cooking combined.
What to do with the therm on your next bill.
Find the therms used
Usually labelled "Therms billed" or "Total therms". This is the energy figure that drives your supply charge.
Spot the correction factor
A small number near 1.0. Multiplied by your CCF meter reading to get therms. Check it has not jumped more than 5% versus last winter.
Convert to kWh in your head
Therms x 30 (close enough to 29.3) gives kWh of energy. Use this when comparing a gas bill to an electric bill.
Use the converter above
Enter your therms, pick your state. The side-by-side dollar comparison shows what the same energy costs through the electric wires.
Considering a heat pump?
Divide your electric rate by the heat pump's COP (use 3 for modern units). Compare that delivered-kWh cost to therm cost divided by 29.3 and your furnace efficiency.
Check state averages
EIA publishes monthly residential gas prices by state. If your $/therm is 25% above your state average, ask your utility why.
Common questions about therms.
A therm is a unit of natural gas energy equal to exactly 100,000 BTU, or about 29.3 kWh. US gas utilities bill in therms because the unit measures the actual heat content of the gas you used, regardless of temperature or pressure variations in the pipes.
One therm equals about 29.3 kWh of energy. So 100 therms of gas contain the same energy as roughly 2,930 kWh of electricity. The two units measure the same thing (energy delivered) at very different scales.
A typical US home that heats with natural gas uses 70 to 90 therms per month on an annual average, with heavy seasonal variation: 150 to 200+ therms in winter, 5 to 15 therms in summer (water heater and stove only). That works out to about 900 therms a year, or roughly $1,300 at the US average price.
Your meter measures volume (cubic feet) but you are billed for energy (therms). The utility multiplies CCF by a monthly BTU correction factor (typically 1.00 to 1.05) that accounts for gas composition and pressure. The factor changes month to month, which is why CCF x rate never matches your therm bill exactly.
Per unit of raw fuel energy, yes — about 3.6x cheaper at US average prices ($1.45/therm vs about $5.25 for the same 29.3 kWh of electricity). But heating efficiency changes the picture. A 95% gas furnace and a heat pump operating at COP 3 deliver heat at roughly the same operating cost, and in states with cheap electricity (ND, WA, NE) the heat pump already wins.
The Energy Information Administration publishes monthly residential natural gas prices for every state at eia.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm. EIA reports prices per Mcf (thousand cubic feet); divide by 10.37 to convert to dollars per therm.