How much heat is in a gallon of propane, a therm of gas or a cord of wood? The chart below gives the heat content of common heating fuels from US government sources, the share that typically ends up as usable heat, and how much of each fuel makes one million Btu. Enter your own prices to compare the cost of heat.
Heat content and usable heat by fuel
| Fuel | Unit | Gross heat, FPL (Btu) | Heat content, EIA (Btu) | Typical efficiency (FPL) | Usable heat (Btu) | Units for 1 million Btu usable |
|---|---|---|---|---|---|---|
| Natural gas | 1,000 cubic feet | 1,025,000 | 1,036,000 | 80% | 820,000 | 1.22 |
| Natural gas | therm | 100,000 | 100,000 | 80% | 80,000 | 12.5 |
| Propane | gallon | 91,300 | 91,452 | 79% | 71,900 | 13.9 |
| Heating oil (#2 fuel oil) | gallon | 138,800 | 138,500 | 83% | 115,000 | 8.70 |
| Electricity (resistance heat) | kWh | 3,412 | 3,412 | 98% | 3,340 | 299 |
| Seasoned firewood (20% moisture) | cord | 20,000,000 | 20,000,000 | 77% | 15,300,000 | 0.065 |
| Premium wood pellets | ton | 16,400,000 | — | 83% | 13,600,000 | 0.074 |
Cost per million Btu: enter your prices
Notes
- Gross vs usable. Gross is all the heat in the fuel. Usable heat allows for what goes up the flue at a typical efficiency; FPL notes its values were developed with commercial boilers in mind, not residential units, so use your own appliance’s rated efficiency where you know it.
- FPL and EIA figures differ slightly (for example propane 91,300 vs 91,452 Btu per gallon); both are shown as published.
- Wood varies by species and dryness. The firewood row is FPL’s seasoned average; see the firewood BTU chart by species and how much firewood you need.
- Electric heat. 1 kWh is 3,412 Btu; see the watts to BTU chart and the space heater cost chart.
Fuel-burning heat safety (CPSC)
- Have a professional inspect all fuel-burning heating systems, including furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents, each year.
- Fuel-burning heating systems can produce carbon monoxide (CO), an odorless, colorless and deadly gas. Put CO alarms on every level of the home and outside sleeping areas, and test them every month.
- For fuel-burning portable heaters, never refuel while in use: turn the heater off and let it cool first.
- Keep portable heaters at least three feet from drapes, furniture, bedding and other combustible materials.
Frequently asked questions
How many BTU are in a gallon of propane?
About 91,500 Btu (EIA: 91,452; FPL: 91,300), or about 71,900 Btu of usable heat at 79% efficiency.
How many BTU are in a gallon of heating oil?
About 138,500 Btu (EIA), 138,800 in FPL’s table, or about 115,000 Btu usable at 83%.
How many BTU are in a therm of natural gas?
100,000 Btu. One cubic foot of natural gas holds about 1,036 Btu (EIA).
Sources
- USDA Forest Service, Forest Products Laboratory. Techline WOE-3, “Fuel Value Calculator” (updated January 2024): gross and net heating values and efficiencies. A US Government work, available from the Forest Products Laboratory, Madison, Wisconsin.
- US Energy Information Administration. “British thermal units (Btu)”, Energy Explained (sample Btu conversion factors), eia.gov, read 12 November 2026.
- US Consumer Product Safety Commission. “Keep Warm and Safe This Winter: Tips for Using Generators, Furnaces and Space Heaters”, news release, 23 January 2026, cpsc.gov.
Last reviewed: 12 November 2026. Numbers in the tables are our arithmetic from the sources listed. How we check our work: methodology and corrections. Spotted an error? Please let us know.