Cost Per BTU Calculator
Heating fuels are sold in units that refuse to be compared: therms, gallons, kilowatt-hours, cords. The only honest common ground is the British thermal unit, and the even more honest version of the comparison prices useful heat after your equipment’s efficiency has taken its cut.
Use Simple mode for one division, total cost over total BTUs. Use Compare mode to rank up to three fuels side by side on dollars per million BTU of useful heat, using standard EIA heat contents and the efficiency you enter for your own furnace, boiler, stove, or heat pump.
Heat contents are standard EIA reference values. Efficiency is your equipment’s rated efficiency: AFUE for furnaces and boilers, or COP times 100 for a heat pump (a COP of 2.5 is 250%).
Simple mode prices the energy in the fuel. Compare mode prices the heat in the room, which is the number that decides real heating bills.
Quick Answer
Key takeaways
- Compare fuels in dollars per million BTU (MMBtu), never in price per gallon, therm, or kilowatt-hour. The units are rigged to be incomparable.
- Raw cost prices the energy in the fuel. Useful cost divides by efficiency and prices the heat in the room. Rankings can flip between the two.
- A heat pump at 250% efficiency is not breaking physics: it moves heat instead of making it, which is why electric heat can win in Compare mode while losing badly as baseboard heat.
- Firewood varies more than any other preset: species and moisture swing a cord from roughly 14 to 24 million BTU, so treat the 22 million preset as a midpoint, not a promise.
How to use the cost per BTU calculator
Simple mode takes two numbers: what you paid and how many BTUs it bought. Reach for it when a bill, a delivery, or a tank refill already tells you both. The answer comes back per BTU and per million BTU, the scale the heating industry actually quotes.
Compare mode is for decisions. Each fuel row takes a price per unit, a quantity, and the efficiency of the equipment that will burn or use it, with the heat content preset from EIA reference values. Add a third fuel with the button, swap any row to a different fuel or to Custom with your own heat content, and the ranking rebuilds on the useful-heat column. When the question widens from one fuel decision to the whole home energy bill, the cost of energy calculator totals consumption across sources, and the cost per gallon calculator handles the liquid-fuel purchases themselves.
The EIA formula, and the efficiency step most tools skip
The method here is the one the U.S. Energy Information Administration publishes for exactly this question.
The efficiency step is not decoration. An 80% AFUE furnace turns 80 cents of every fuel dollar into room heat and sends 20 cents up the flue, so its useful cost is the raw cost divided by 0.80, a 25% penalty. Resistance electric heat converts at 100% and pays no penalty, but starts from a far higher raw price. A heat pump sidesteps the frame entirely: at a COP of 2.5 it delivers 250% efficiency by moving outdoor heat indoors, which is why the heat pump preset can beat gas in this table while baseboards lose to it. The EIA’s own worked examples in its energy units and calculators guide make the same point with neighboring houses burning gas and oil.
Worked examples, checked against this exact tool
Simple mode is pre-filled with $150 for 1,500,000 BTU: $150 / 1,500,000 = $0.000100 per BTU, which is $100.00 per million BTU raw.
Compare mode is pre-filled with a realistic winter pairing:
| Fuel | Inputs | Total BTU | Raw $/MMBtu | Useful $/MMBtu |
|---|---|---|---|---|
| Natural gas | $1.39 per therm x 15, 80% furnace | 1,500,000 | $13.90 | $17.37 Winner |
| Electricity (baseboard) | $0.20 per kWh x 2,000, 100% | 6,824,000 | $58.62 | $58.62 |
Read the table the way the tool ranks it: gas buys useful heat at $17.37 per million BTU, electricity at $58.62. Swap the electricity row to the Electric heat pump preset at the same $0.20 per kWh and its useful cost falls to about $23.45 per MMBtu, still behind this gas price but suddenly competitive, which is the single most instructive experiment this page offers. Airflow equipment obeys a different cost logic, priced by the cubic foot moved rather than heat delivered; the cost per CFM calculator covers that side of the HVAC ledger.
The heat contents behind the presets
Every preset in Compare mode carries the heat content the tool has always used, drawn from EIA reference values. The EIA revises its conversion factors periodically (its current table lists heating oil at 138,500 BTU per gallon and propane at 91,452, a shade under the long-used values below, and firewood at 20,000,000 BTU per cord against the 22,000,000 midpoint preset used here), so treat the last few hundred BTU as rounding at the scale of a heating season.
| Fuel | Unit | Heat content in this tool | Default efficiency |
|---|---|---|---|
| Natural gas | therm | 100,000 BTU | 80% |
| Electricity | kWh | 3,412 BTU | 100% |
| Electric heat pump | kWh | 3,412 BTU | 250% |
| Propane | gallon | 91,333 BTU | 80% |
| Heating oil #2 | gallon | 138,690 BTU | 80% |
| Kerosene | gallon | 135,000 BTU | 80% |
| Firewood | cord | 22,000,000 BTU | 60% |
| Wood pellets | ton | 16,500,000 BTU | 80% |
| Coal (anthracite) | ton | 25,000,000 BTU | 75% |
The Penn State energy curriculum’s heating values table tells the same story from the classroom side, and the Engineering ToolBox energy content reference is a handy cross-check when a supplier quotes an unusual fuel. Wood is the honest exception in every table: a cord of seasoned oak and a cord of green softwood are different fuels wearing the same name, which is why the Custom row exists.
What competing calculators miss
The standard price-per-BTU tool converts units and compares two fuels on raw cost, then stops. Four gaps follow from that.
Miss 1: raw cost crowns the wrong winner. Without the efficiency division, an 80% furnace and a 98% condensing furnace price identically, and a heat pump looks like expensive electricity. Useful cost is the ranking that matches your bill.
Miss 2: two-fuel limits. Real decisions are three-way: keep the furnace, add a heat pump, or fall back to the stove. This tool ranks three at once and marks the winner.
Miss 3: hidden heat contents. Tools that never publish their BTU-per-unit assumptions cannot be audited. Every preset here is printed in the table above with its source tradition named.
Miss 4: no simple mode. Sometimes you already hold a total cost and a total BTU figure from a bill or a tank gauge, and a fuel-row builder is overkill. One division should take one division’s worth of effort.
Frequently Asked Questions
Divide the total cost by the total BTUs. For fuel comparisons, the EIA form is price per unit divided by heat content per unit, multiplied by 1,000,000 to get dollars per MMBtu, then divided by efficiency for the useful-heat figure.
One million BTUs. Individual BTUs are too small to price sensibly (the Simple example is $0.000100 each), so the industry quotes heating costs per million BTU, written MMBtu, where the first M is the Roman numeral for a thousand.
100,000 BTU, by definition. A therm is defined as 100,000 BTU, which is why natural gas rows in this tool need no conversion fudge, though the gas in the pipe varies slightly around that figure in practice.
3,412 BTU. This one is exact: a kilowatt-hour of electricity converted entirely to heat yields 3,412 BTU, which is the figure the EIA and this tool both use for electricity and heat pump rows.
Because you buy heat in the room, not energy in the fuel. An 80% furnace wastes a fifth of every dollar, raising its useful cost by 25% over raw. A heat pump at 250% efficiency cuts its useful cost to 40% of raw. Those two swings are larger than most price differences between fuels.
It depends on your local prices and your equipment, which is the honest answer this tool is built around. At the pre-filled prices, gas in an 80% furnace wins at $17.37 per useful MMBtu against $58.62 for baseboard electric and about $23.45 for a heat pump. Enter your own tariff and the ranking may change.
Often on raw cost, yes, and the preset 22 million BTU per cord at a low cord price is hard to beat. A 60% efficient stove, plus the labor of handling wood, narrows the gap, and green or softwood cords carry far fewer BTUs than the preset assumes. Run your actual cord price and species through the Custom row for a fair test.
From U.S. Energy Information Administration reference values, the standard source for U.S. fuel comparisons. The EIA updates its conversion factors over time, so current EIA tables can differ by a few hundred BTU per unit from the long-used presets in this tool, an immaterial difference across a heating season.
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References
- U.S. Energy Information Administration, “How do I compare the cost of heating fuels?”: the official formula, price divided by heat content times 1,000,000, and the role of appliance efficiency. EIA: How do I compare the cost of heating fuels?. Accessed October 2026.
- U.S. Energy Information Administration, “Energy units and calculators explained”: sample BTU conversion factors (electricity 3,412 BTU per kWh, natural gas 100,000 BTU per therm) and worked house-to-house comparisons. EIA: Energy units and calculators explained. Accessed October 2026.
- U.S. Energy Information Administration, “How do I convert natural gas prices to dollars per BTU or therm?”: heat content of delivered natural gas and conversions between $/Ccf, $/therm, and $/MMBtu. EIA: Converting natural gas prices. Accessed October 2026.
- Penn State, EGEE 102 “Fuel Choices”: heating values of common fuels table used in energy conservation teaching, cross-checking the presets in this tool. Penn State EGEE 102: Fuel choices and heating values. Accessed October 2026.
- Engineering ToolBox, “Energy Content in common Energy Sources”: independent heat-content reference for fuels from butane to wood pellets. Engineering ToolBox: Energy content in common energy sources. Accessed October 2026.