Propane Usage Calculator
See how many gallons of propane an appliance burns a day, how long a tank lasts and what a month costs. A propane usage calculator for 20 lb to 1,000 gal tanks.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Propane used per day
- 6.99 gal
- 80,000 BTU/h running 8 h a day is 640,000 BTU, and a gallon of propane holds 91,502 BTU. That is 212.6 gal a month
- Days a full tank lasts
- 57.2 days
- A water capacity of 500 gal filled to 80 percent holds 400 gal. Run the appliance fewer hours in shoulder weather and the same fill stretches well past this
- Cost per month
- $585
- 212.6 gal at $2.75 per gallon. At this rate a 180 day heating season comes to $3,462 before tank rent and delivery fees
- Days to the refill call
- 35.7 days
- The gauge reads 80%, which leaves 250 gal above the 30 percent line. Most suppliers want the call at 30 percent so the truck arrives on a routed day, not an emergency run
- Usable capacity
- 400 gal
- NFPA 58 caps the fill at 80 percent of the 500 gal water capacity so the liquid has room to expand. The gauge reads that water capacity, so 80 percent is a full tank
- Planning estimate
- Verify on site
- Appliance input ratings, run hours and weather all move this number. Tank siting, gas piping and leak testing are the work of a licensed LP gas fitter, and the local inspector governs
Propane Usage formula
Gallons per day = BTU per hour x Hours per day / 91,502
Usable gallons = Tank water capacity x 0.80 (the NFPA 58 fill limit)
Days per fill = Usable gallons / Gallons per day
Gallons above the 30% call = (Gauge % - 30) / 100 x Tank water capacityWorked example
A tankless water heater rated 150,000 BTU per hour, firing about 1.5 hours a day for a family of four, on a 250 gallon tank at $3.10 a gallon. Daily burn is 150,000 x 1.5 = 225,000 BTU, divided by 91,502, which is 2.46 gallons a day. Over an average month that is 2.46 x 30.4 = 74.8 gallons, or $232.
The tank holds 250 x 0.80 = 200 usable gallons, so a full fill runs 200 / 2.46 = 81.3 days. If the gauge reads 70 percent today, the propane above the 30 percent refill line is (70 - 30) / 100 x 250 = 100 gallons. That is another 40.7 days before the call. Add a furnace to the same tank and that window closes to under two weeks in January.
Quick reference
| Appliance | BTU per hour | Hours per day | Gallons per day | Days on 400 gal |
|---|---|---|---|---|
| Furnace | 80,000 | 8 | 6.99 | 57 |
| Water heater, tank | 40,000 | 3 | 1.31 | 305 |
| Water heater, tankless | 150,000 | 1 | 1.64 | 244 |
| Range | 65,000 | 1 | 0.71 | 563 |
| Clothes dryer | 22,000 | 1 | 0.24 | 1,664 |
| Gas fireplace | 26,000 | 4 | 1.14 | 352 |
| Standby generator | 200,000 | 24 | 52.46 | 8 |
| Pool heater | 250,000 | 6 | 16.39 | 24 |
| Grill | 30,000 | 1 | 0.33 | 1,220 |
What a gallon of propane buys
Propane holds 91,502 BTU per gallon and 21,548 BTU per pound, so the arithmetic is short. Take the appliance input in BTU per hour, divide by 91,502, and you have gallons per hour. An 80,000 BTU per hour furnace burns 0.87 gallons an hour of actual burner time. Eight hours of firing on a January day is 6.99 gallons. The number people get wrong is hours, not gallons. A furnace sized correctly runs 8 to 12 hours out of 24 at design temperature, and maybe 3 in October. A single daily figure describes one kind of weather.
Input ratings are on the rating plate and they are input, not output. A furnace with an 80,000 BTU/h input at 95 percent efficiency delivers 76,000 to the house, but it still burns fuel for the full 80,000. Common residential inputs run 40,000 to 120,000 for a furnace and 30,000 to 50,000 for a tank water heater. A tankless is 120,000 to 199,000, a range with the oven on about 65,000, and a dryer 18,000 to 25,000. A 22 kW standby generator is the outlier at roughly 200,000 BTU/h on half load, which is why a week of outage empties a 500 gallon tank.
Tank size, the 80 percent rule and when to call
Every propane tank is sized by water capacity and filled to 80 percent of it. Liquid propane expands nearly 17 times more than water for the same temperature rise, and the vapor space absorbs that. So a 500 gallon tank holds 400 gallons, a 250 holds 200 and a 120 holds 96. A 20 pound grill cylinder works out to about 4.6 gallons. The float gauge on the dome reads percent of water capacity, not percent of what is burnable. So 80 percent is a full tank, and 40 percent is half a fill, or 200 gallons on a 500.
Call for a delivery at 30 percent. Suppliers route trucks by area, and a tank at 30 percent can wait for the routed day instead of an emergency run that typically costs $75 to $150 extra. The other reason to stay above 30 is vaporization. A tank makes vapor off the liquid surface, and the colder the weather and the lower the liquid level, the less surface and the less vapor. A 500 gallon tank has margin; a pair of 100 pound cylinders feeding a furnace at 10 degrees F does not, and the burner drops out on low pressure. That failure looks exactly like an empty tank and is usually neither.
What this calculator leaves out
This is fuel arithmetic, not a heating load. It does not run a Manual J on your house, weight the season by degree days, or model an appliance cycling on a thermostat. Standing pilot losses on an older fireplace or water heater are not in it, and they can be 500 to 800 BTU/h around the clock. On the money side it leaves out tank rent, the delivery or hazmat fee, and the minimum drop most suppliers require. First-fill and will-call rates, budget plans and prebuy contracts are also outside it. It does not size the tank to the appliance load, set the regulator stages, or size the gas piping, all of which come from NFPA 54 and the supplier. Tank placement clearances and the leak test after a run-out are the licensed gas fitter's work.
Code limits that apply
- NFPA 58 filling limitchecked
A container is filled to 80 percent of water capacity so the liquid can expand
If you miss it: An overfilled tank pushes liquid out through the relief valve as the day warms, and it can ignite at the vent
- NFPA 58 tank spacing
A 125 to 500 gal tank sits at least 10 ft from a building opening and the property line
If you miss it: A tank set too close to a window or dryer vent is red-tagged and the supplier will not fill it
- NFPA 58 OPD valve
Cylinders from 4 to 40 lb need an overfill prevention device, marked by a triangular handwheel
If you miss it: A pre-1998 round-handle cylinder is turned away at every filling station in the US
- DOT cylinder recert
A grill cylinder is requalified 12 years after manufacture, then on a 5 or 10 year cycle
If you miss it: An out-of-date collar date means no refill, so the cylinder can only be exchanged
- NFPA 54 restoring gas
After a run-out the system is leak tested and every pilot relit before gas is turned back on
If you miss it: Gas restored to an open valve fills the room with vapor that settles at floor level
Rows marked checked produce a warning in the results when an entry crosses the limit. The others are on the plans or on site and this calculator does not test them. Local amendments can be stricter; the adopted edition and the inspector govern.
Mistakes that cost money
- Reading the float gauge as gallons. It shows percent of water capacity, so 40 percent on a 500 gal tank is 200 gallons.
- Waiting past 30 percent to call. An off-route emergency fill typically adds a $75 to $150 fee on top of the gallons.
- Letting a tank run dry. NFPA 54 requires a leak test and a relight of every pilot, which is a billed service call.
- Running a furnace off 100 lb cylinders. In freezing weather they cannot vaporize fast enough and the burner locks out on low pressure.
- Comparing suppliers on price per gallon alone, with no tank rent, delivery fee or minimum drop, which typically runs 100 to 150 gallons.
- Storing a spare grill cylinder indoors or in a basement. Propane vapor is heavier than air and pools at floor level.
Key facts
- One gallon of liquid propane holds 91,502 BTU and one pound holds 21,548 BTU, so propane carries less heat per gallon than heating oil or gasoline.
- NFPA 58 limits a propane container to 80 percent of its water capacity so the liquid can expand, which is why a 500 gallon tank holds 400 usable gallons.
- A 20 pound grill cylinder holds about 4.6 gallons of propane, roughly 421,000 BTU, not the 5 gallons its size suggests.
- A gallon of liquid propane weighs about 4.24 pounds at 60 degrees F, so tanks are filled by weight at the plant and billed by the gallon at the house.
- An 80,000 BTU per hour furnace burns 0.87 gallons of propane for every hour the burner is actually firing.
Frequently asked questions
How long will a 500 gallon propane tank last?
A 500 gallon tank holds 400 usable gallons. Heating alone with an 80,000 BTU per hour furnace running 8 hours a day, that is 57 days. Add a water heater, range and dryer and the same fill covers roughly 6 to 8 weeks of deep winter, or a full mild season.
How many gallons are in a 20 lb propane tank?
About 4.6 gallons, not 5. The cylinder is filled to 80 percent of its capacity so the liquid can expand, which works out to roughly 421,000 BTU. A three burner grill rated 30,000 BTU per hour runs about 14 hours on one.
At what percentage should I refill a propane tank?
Call at 30 percent. That leaves time for a routed delivery instead of an emergency fill, and keeps enough liquid surface for cold-weather vaporization. It also avoids the leak test and pilot relight a run-out forces.
Why does my propane run out of pressure when it is cold?
A tank makes vapor off the surface of the liquid, and cold liquid at a low level cannot vaporize fast enough for a big burner. It shows up as a furnace that locks out on a cold morning with fuel still in the tank, and it is most common on 100 lb cylinders.
Sources and references
- Fuel Properties Comparison, propane energy content per gallon (U.S. Department of Energy Alternative Fuels Data Center)
- British thermal units and the Btu content of common fuels (U.S. Energy Information Administration)
- NFPA 58 Liquefied Petroleum Gas Code, container filling limits (NFPA)
- Residential tank water heaters, gas input ratings (Rheem)
Next steps for this project
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.