Calculator
Propane usage calculator
Gallons per hour, month, and year from an appliance's Btu rating, with tank life and refill frequency.
Propane carries about 91,452 Btu per gallon, per the EIA energy conversion tables, so gallons are total Btu input ÷ 91,452. Cylinder sizes use 4.24 lb of propane per gallon: a properly filled 20-lb cylinder holds about 4.7 gallons. Tank sizes are nominal shell capacity; tanks fill to at most 80% (the 80% rule) and the gauge reads percent of the shell. The state price is the EIA weekly state residential survey figure, published October through March; between surveys the last surveyed price prefills, labeled with its date, and stays editable. Everything here is arithmetic on the numbers you enter — weather, burner cycling, appliance condition, and gauge accuracy all move real usage. It is an estimate, not delivery scheduling, tank sizing, or safety advice.
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How propane usage is calculated
Gas appliances are rated by Btu input per hour — the fuel energy the burner draws when it fires, printed on the nameplate or spec sheet. Propane carries about 91,452 Btu per gallon, so consumption is one division:
gallons = Btu per hour × burner hours ÷ 91,452
A 100,000 Btu furnace burns about 1.09 gallons per hour of burner time. The number that takes judgment is the hours: a furnace that is "on" for ten hours may fire the burner for only four or five of them, which is what the duty-cycle field represents. Entering actual burner-on hours pairs with a 100% duty cycle; entering thermostat or schedule hours pairs with a lower one.
One caution on the rating itself: nameplates list input Btu. The heat delivered to the room is lower by the appliance's efficiency, and this calculator wants the input figure — an output rating understates fuel use, and discounting an input rating by efficiency double-counts it.
Propane gallons per hour by Btu rating
At full input, consumption scales directly with the rating:
| Btu input rating | Gallons per hour |
|---|---|
| 30,000 (fireplace insert, cooktop) | 0.33 |
| 50,000 (patio heater, small furnace) | 0.55 |
| 75,000 (tankless water heater, mid furnace) | 0.82 |
| 100,000 (whole-home furnace) | 1.09 |
| 150,000 (large furnace, boiler) | 1.64 |
| 200,000 (pool heater, low end) | 2.19 |
| 400,000 (pool heater, high end) | 4.37 |
Real appliances cycle and modulate, so average consumption over a day usually sits well below the full-input rate.
How long a propane tank lasts
Tank names refer to nominal shell capacity, and a tank is filled to at most 80% of it, so a "500-gallon" tank holds about 400 gallons full. The gauge reads percent of the shell: a 60% reading on a 500-gallon tank is 300 gallons. The Tank life tab counts the gallons between the current reading and a reserve level you pick, then divides by daily use — 300 gallons down to a 20% (100-gallon) reserve is 200 usable gallons, about 50 days at 4 gallons a day.
What changes actual usage
The arithmetic is exact; the inputs are the estimate. Outdoor temperature drives furnace burner hours more than any other factor, which is why the same house burns three times the propane in January as in March. Insulation, air leakage, and thermostat setting move the runtime; appliance age and condition move the efficiency; hot-water demand and generator load vary week to week; and float-style tank gauges read coarsely, commonly a few points off. The result on this page is the arithmetic of the numbers entered, not a metered reading.
Common questions
How do you calculate propane usage from a Btu rating?
Multiply the appliance's Btu input rating by its burner-on hours, then divide by 91,452 — the Btu in a gallon of propane. A 100,000 Btu furnace that fires 4 hours a day burns about 4.4 gallons a day. Use the input rating from the nameplate, not the heat output.
How many gallons of propane does a 100,000 Btu appliance use per hour?
About 1.09 gallons for each hour the burner fires at full input (100,000 ÷ 91,452). Cycling and modulation usually put average use below that, which is what the duty-cycle field accounts for.
How long will a 500-gallon propane tank last?
It depends on the gauge reading and the burn rate, not the tank name alone. At a 60% gauge a 500-gallon tank holds about 300 gallons; run down to a 20% reserve that is 200 usable gallons — 50 days at 4 gallons a day, 100 days at 2. The Tank life tab runs this count for any size, gauge, and usage rate.
How much propane does a generator use?
It varies with the generator's size and the electrical load it carries, not just its rating — a 22 kW standby unit commonly burns 2 to 3.5 gallons an hour between half and full load. Manufacturer fuel-consumption tables list gallons per hour at half and full load; those figures times expected run hours convert directly in the Appliance usage tab.
How much propane is in a 20-pound cylinder?
About 4.7 gallons when properly filled: propane weighs about 4.24 pounds per gallon, and 20 ÷ 4.24 ≈ 4.7. Actual fill varies a little with temperature and filling equipment.
Why does actual usage differ from the estimate?
The formula is exact, but the inputs move: outdoor temperature swings burner hours, appliances cycle and modulate below their rated input, equipment condition drifts, and tank gauges read coarsely. Weeks of identical settings can burn noticeably different gallons.