Why fuels cannot be compared without a heating value
A gallon is a volume, a ton is a mass and a kilowatt-hour is already an energy — so putting them on the same axis needs one number per fuel: the heating value, the energy released when a unit of that fuel burns completely. Multiply your quantity by that number and every fuel becomes comparable.
This matters in three routine situations. When you reconcile a utility bill, the gas company measures cubic feet at the meter but bills therms, applying a monthly BTU factor that you can check. When you benchmark a building, you must convert every fuel to a single site-energy figure before you can compute energy use intensity in kBtu per square foot per year. And when you consider switching fuels, the only fair starting comparison is dollars per million BTU, which requires converting both fuels first.
The unit soup is worse than it looks. "CCF" means one hundred cubic feet, not one cubic foot. A therm is a fixed 100,000 BTU regardless of gas quality, so a ccf and a therm are close but not equal — a ccf of typical pipeline gas is about 1.037 therms. A "ton" of pellets in the United States is a 2,000 lb short ton, not a 2,205 lb tonne. And a cord of firewood is a stacked volume of 128 cubic feet, so its energy content depends entirely on what species filled it and how dry the wood is.
Higher versus lower heating value, and why it changes the answer by 10%
Burning a hydrocarbon produces water vapour. The higher heating value counts the energy you would recover if that vapour condensed back to liquid and gave up its latent heat; the lower heating value does not. The gap is the latent heat of the water formed, and it is largest for fuels richest in hydrogen — about 10 percent for natural gas, around 6 to 7 percent for diesel and fuel oil, and effectively zero for electricity.
Use HHV in the United States. Utility billing, EIA statistics, the therm itself, AFUE furnace ratings and the Uniform Energy Factor for water heaters are all on a gross basis. Mixing an LHV energy figure with an HHV-based efficiency inflates apparent performance by roughly the size of the gap, which is exactly how a condensing boiler ends up quoted at "105% efficient" — that number is thermal efficiency on an LHV basis, and the same boiler is about 95 percent on HHV.
Use LHV when the source you are comparing against does. European engine and turbine ratings, most combustion research and many international energy statistics are net-basis. The LHV figures in this calculator are the standard higher heating values scaled by a typical ratio for each fuel family, so treat them as approximate; if you need a precise net value for a specific fuel, take it from a fuel-property table or an assay rather than from a ratio.
Worked example: a winter gas bill and its propane equivalent
Your December gas bill shows 187 ccf. You want to know the energy, the cost per million BTU at $1.55 per therm, and how much propane would have done the same job if you converted the house.
- Convert ccf to BTU. One ccf is 100 cubic feet, and pipeline gas averages 1,037 BTU per cubic foot, so one ccf is 103,700 BTU. 187 × 103,700 = 19,391,900 BTU.
- Express as MMBtu. 19,391,900 ÷ 1,000,000 = 19.39 MMBtu.
- Express as therms. 19,391,900 ÷ 100,000 = 193.9 therms. Notice this is more than the 187 ccf — that 3.7 percent gap is the whole reason your utility publishes a BTU factor.
- Express as kWh. 19,391,900 ÷ 3,412.14 = 5,683 kWh, and as gigajoules, 19,391,900 ÷ 947,817 = 20.46 GJ.
- Cost per MMBtu. 193.9 therms × $1.55 = $300.55, and $300.55 ÷ 19.39 MMBtu = $15.50 per MMBtu. That $15.50 is the number to carry into any fuel comparison.
- Propane equivalent. 19,391,900 ÷ 91,500 BTU per gallon = 211.9 gallons. At $2.80 a gallon that is $593, or $30.60 per MMBtu — nearly double the gas cost for identical delivered heat.
Feed that $15.50 per MMBtu into the water heating cost calculator or the insulation payback calculator and every downstream dollar figure follows from it.
Standard higher heating values by fuel
| Fuel | Billing unit | HHV per unit | MMBtu per unit | kWh per unit |
|---|---|---|---|---|
| Natural gas | cubic foot | 1,037 BTU | 0.001037 | 0.304 |
| Natural gas | ccf (100 ft³) | 103,700 BTU | 0.1037 | 30.39 |
| Natural gas | therm | 100,000 BTU | 0.100 | 29.31 |
| Propane (LPG) | gallon | 91,500 BTU | 0.0915 | 26.82 |
| #2 fuel oil | gallon | 138,500 BTU | 0.1385 | 40.59 |
| Diesel | gallon | 137,400 BTU | 0.1374 | 40.27 |
| Gasoline | gallon | 120,300 BTU | 0.1203 | 35.26 |
| Kerosene | gallon | 135,000 BTU | 0.1350 | 39.57 |
| Electricity | kWh | 3,412 BTU | 0.003412 | 1.00 |
| Seasoned hardwood | cord | 20,000,000 BTU | 20.0 | 5,861 |
| Wood pellets | short ton | 16,500,000 BTU | 16.5 | 4,835 |
| Bituminous coal | short ton | 24,000,000 BTU | 24.0 | 7,033 |
kWh columns are the HHV divided by 3,412.14. Use these for energy accounting, never for appliance output — a wood stove delivers 60-80% of a cord's energy into the room while a condensing boiler delivers over 90% of a therm.
How to read the result
The MMBtu figure is the one to carry forward. Building benchmarking, energy audits and utility programs all normalise to MMBtu or kBtu, so once you have converted every meter into MMBtu you can add them, divide by floor area, and compare a school in Maine against one in Arizona.
Divide cost by MMBtu before comparing fuels. A gallon of propane at $2.80 and a therm of gas at $1.55 look like the propane is twice as expensive; on an energy basis it is $30.60 versus $15.50 per MMBtu, so it is closer to double than the raw prices suggest, and the gap only shows up after the conversion.
Remember that site energy is not delivered heat, and neither is source energy. This calculator reports the chemical energy you bought. What reaches the room is that figure times the appliance efficiency. What was consumed to produce it — the fuel burned at a power plant to make your kWh, including line losses — is a larger source-energy number, and the conversion between the two is a separate calculation entirely.
Barrels of oil equivalent are a reporting convention, not a physical barrel. The EIA defines one BOE as 5.8 million BTU. It is used in oil-and-gas reserve reporting and in corporate energy disclosures, and it does not correspond to any grade of crude you can buy.
Where conversions usually go wrong
- Treating a ccf as a therm. They differ by whatever the local BTU factor is, typically 2 to 5 percent. Over a year on a large account that is real money.
- Mixing HHV energy with LHV efficiency. This is the single most common error in combustion analysis, and it flatters the equipment by about the size of the latent-heat gap.
- Assuming a cord is a cord. A face cord or rick is typically a third of a full cord, and softwood carries roughly half the energy of dense hardwood at the same volume.
- Confusing short tons with tonnes. A metric tonne is 2,204.6 lb, about 10 percent more than the 2,000 lb short ton used for US pellet and coal pricing.
- Comparing purchased energy with useful heat. Energy equivalence tells you nothing about what the appliance does with it. Always apply the efficiency of the specific device.
- Using a national average heat content for a specific bill. Utilities publish their actual monthly BTU factor. Enter it in the override field when precision matters.
Key terms
- Therm
- Exactly 100,000 BTU. A billing unit, not a physical quantity of gas — the utility converts your metered cubic feet into therms using a measured heat content factor.
- Ccf
- One hundred cubic feet of gas at standard conditions. Typical pipeline gas at 1,037 BTU/ft³ makes one ccf about 1.037 therms.
- MMBtu
- One million BTU. The M is the Roman numeral for a thousand, so MM is a thousand thousand. Also written dekatherm (10 therms = 1 MMBtu).
- Cord
- A stacked volume of firewood measuring 128 cubic feet, conventionally 4 ft × 4 ft × 8 ft including the air between the pieces.
- Barrel of oil equivalent
- 5.8 million BTU, an EIA reporting convention for aggregating oil, gas and liquids production into one figure.
What to do with the number next
Energy content is the input to almost every other calculation on this site's energy pages. Price it and you get cost per MMBtu, which drives the fuel-switching comparison in the water heating calculator and the savings side of the insulation payback calculator. Multiply it by an emission factor and you get greenhouse gas emissions, which is how the household carbon footprint calculator handles gas, propane and oil, and how the driving CO2 calculator handles a gallon of gasoline.
Two things this converter will not tell you. It will not tell you the source energy or primary energy behind a kilowatt-hour: burning fuel at a thermal power station and moving the electricity to your meter consumes roughly three times the energy that arrives, and different benchmarking programs apply different site-to-source factors. And it will not tell you emissions, because carbon intensity per MMBtu differs sharply between fuels — coal is roughly double natural gas per unit of heat, and electricity depends entirely on the grid that made it.
If you are building an energy model, convert everything to MMBtu first, keep the conversion factors in one place, and record which basis you used. A spreadsheet that mixes HHV gas with LHV oil is wrong by several percent in a way nobody will find later.