Propane tank size calculator

How the propane use and the tank are calculated

This page turns the input of each gas appliance and the hours it runs into the gallons of propane burned in a day, then sets that against the usable volume of a standard tank to give the days between fills. It also checks the connected load against the vaporization capacity of the tank at the lowest winter temperature. Propane's heating value, the appliance load table and the vaporization table come from the Propane Education & Research Council's Technical Pocket Guide. Suppliers quote the 80 percent fill. Tank placement, the regulator and the pipe are outside the page, and the gas pipe sizing calculator covers the pipe.

Energy content

91,500 BTU per gallon of propanePERC Table 1C gives 91,500 BTU per gallon, and Table 1A prints 91,502 with 4.2 lb per gallon at 60°F. The default day burns 1,000,000 BTU, which is 10.93 gallons.

Daily use

gallons per day = sum of (input BTU/h x hours per day) / 91,500The default set is a typical single-family set built from the input ratings of Table 3A, a 100,000 BTU/h furnace for 8 hours, a 50,000 BTU/h water heater for 2 hours, a 65,000 BTU/h range for 1 hour and a 35,000 BTU/h dryer for 1 hour. Only the input ratings come from the guide. The choice of appliances and the hours are this page's illustration.

Monthly use

gallons per 30 days = gallons per day x 30The default comes to 327.9 gallons in 30 days. That figure is only as good as the hours, so a cold month needs the hours of a cold month.

Usable volume

usable gallons = water capacity x 0.8Ferrellgas and AmeriGas both multiply the water capacity by 0.8. That gives 96, 200, 400 and 800 gallons for the 120, 250, 500 and 1,000 gallon tanks.

Days between fills

days = usable gallons x (1 - reserve) / gallons per dayA 500 gallon tank holds 400 gallons. With 20 percent kept in reserve, 320 gallons are used between fills, and at 10.93 gallons a day that lasts 29.3 days.

Gas flow

SCFH = connected load BTU/h / 2,488PERC divides the BTU/h load by 2,488 to get standard cubic feet per hour. The default 250,000 BTU/h is 100.5 SCFH at the full connected load. Carry the connected load of 250,000 BTU/h to the gas pipe sizing calculator, which takes the load in BTU/h, not the SCFH.

Vaporization

capacity = PERC Table 5 value for the tank and the design low, times 0.25 for continuous loadingLiquid propane has to boil off fast enough to feed the appliances. A 500 gallon tank at 0°F gives 300,100 BTU/h in Table 5, which covers the 250,000 BTU/h load with 50,100 BTU/h to spare. The table assumes a tank that is half full.

Worked examples

The default case is a typical single-family set built from the input ratings of Table 3A in the guide, a 100,000 BTU/h furnace, a 50,000 BTU/h water heater, a 65,000 BTU/h range and a 35,000 BTU/h dryer. That is 250,000 BTU/h connected, or 100.5 SCFH when divided by 2,488. With 8, 2, 1 and 1 hours at full input, the day burns 1,000,000 BTU, which is 10.93 gallons at 91,500 BTU per gallon. These input numbers come from the guide. Our choice of appliances and the hours are this page's illustration, and the guide gives no duty cycle.

The table below is Table 5 of the guide, the maximum intermittent withdrawal in BTU/h without tank frosting, for the lowest outdoor temperature averaged over 24 hours. It assumes a half-full aboveground tank at 70 percent relative humidity. For 500 gallons at 0°F it reads 300,100 BTU/h, 50,100 BTU/h above the default load, and 180,600 BTU/h for a 250 gallon tank, which falls 69,400 BTU/h short.

Eight cases below run through the same function the form uses. Four of them keep the default load and change the tank, the winter low or the loading. At -20°F the 500 gallon tank gives 242,300 BTU/h, 7,700 BTU/h under the load, and under continuous loading it gives 75,025 BTU/h. A 1,000 gallon tank lasts 58.6 days and a 250 gallon tank 14.6 days.

Standards and data sources

• Propane Education & Research Council, The Propane Technical Pocket Guide (4482-BR-21, 2021) - Table 1A and Table 1C for the 91,500 BTU per gallon heating value and the 2,488 BTU per cubic foot. The approximate input of typical appliances is in Table 3A, which the guide reprints from NFPA 54-2018. Table 4 for the tank water capacities, and Table 5 for the vaporization rates of 150, 250, 500 and 1,000 gallon tanks from 40°F down to -30°F, with the factor of 0.25 for continuous loading.
• Ferrellgas, How to Choose the Right Propane Tank Size - The 80 percent maximum capacity of most tanks, and the propane held by each size, which is 96 gallons in a 120 gallon tank, 200 in a 250, 400 in a 500 and 800 in a 1,000 gallon tank.
• AmeriGas, Grasping the 80 Percent Fill Rule for Propane Tanks - The rule that the fill capacity is the tank's total capacity multiplied by 0.8, and the reason for it, a cushion of space against the pressure that builds in a hot tank.
• NFPA 58, Liquefied Petroleum Gas Code, and NFPA 54, National Fuel Gas Code - The codes that govern where a container goes, how far it sits from buildings, how it is filled, and how the regulator and the piping are installed. This page does not reproduce their text, and the authority having jurisdiction and the propane supplier apply them to the site.

Limitations of this calculator

• The hours a day are yours. No open source gives a duty cycle for a furnace or a water heater, so the gallons per day are only as good as the hours entered. The default hours (8, 2, 1 and 1) are an illustration, and a real quote uses the heat loss, the climate and the household.
• The vaporization check comes from one table. PERC Table 5 covers 150, 250, 500 and 1,000 gallon aboveground tanks, one-half full, at 70 percent relative humidity, with a 24 hour average low. The form offers only the 250, 500 and 1,000 gallon columns, and the 120 and 2,000 gallon tanks have no column, so the page gives no figure for them. An underground tank holds a steadier temperature, and its rate is not in the table.
• Temperatures step every 10°F and the page never interpolates. Pick the row at or below the coldest 24 hour average at the site. A short colder snap is not the same as a 24 hour average, and the supplier knows the local record.
• The table assumes a tank one-half full. With a reserve of up to 60 percent of the usable volume, the tank holds at most 48 percent of its water capacity at refill, which is always below that half, and the page says so whenever it checks vaporization. A tank with less liquid has less wetted surface and vaporizes less. The table is a rule of thumb, as the guide itself says, and the maker's rating of the tank takes precedence.
• The 80 percent is the fill that suppliers quote for the water capacity. NFPA 58 and the filler's gauge decide the limit on the day, and the table of maximum filling density in the code depends on the container and the temperature. The page uses 0.8 for every size.
• One tank. Two tanks manifolded together add their volumes, but the page does not model their combined vaporization or their balance. Portable cylinders of 20 pounds and 100 pounds are not covered, since their fill is by weight and their vaporization is a separate question.
• Tank placement is not covered. The distance from buildings, property lines, ignition sources and openings, the burial depth of an underground tank, the regulator and the piping all come from NFPA 58 and NFPA 54 and from the authority having jurisdiction.
• Price, delivery minimums and contract terms are outside the page, and so is a propane supplier's own tank rental or purchase rule. Ask the supplier.
• This is a planning estimate, not a design drawing. A licensed propane contractor, the manufacturer's data and the authority having jurisdiction decide the installation.

Common propane tank sizing mistakes

1. Counting the water capacity as propane. A 500 gallon tank is a water capacity. Suppliers fill it to 80 percent, so it holds 400 gallons of propane, a 250 gallon tank holds 200 and a 1,000 gallon tank holds 800. On the default load of 10.93 gallons a day, the 500 gallon tank's 320 usable gallons last 29.3 days, where the full 500 gallons would have promised more.
2. Taking the BTU/h load as a daily load. The 250,000 BTU/h of the default set is the rate when everything fires together. Divided by 91,500 it gives 2.73 gallons an hour at full input, and the day burns 10.93 gallons because the appliances run the equivalent of 4 hours at full input. Dividing the load by the heating value alone says nothing about a day.
3. Sizing for the average and forgetting the cold morning. The tank may hold plenty of propane and still be unable to turn enough of it to gas. At 0°F a 250 gallon tank gives 180,600 BTU/h in PERC Table 5, 69,400 BTU/h short of the default 250,000 BTU/h load, while a 500 gallon tank gives 300,100 BTU/h and a 1,000 gallon tank 534,500 BTU/h. The guide's section on vaporization says to consider the lowest winter temperature at the location.
4. Choosing the design low from a winter average. Table 5 is built on the lowest 24 hour average. Moving the same 500 gallon tank from 0°F to -20°F drops the rate from 300,100 to 242,300 BTU/h, which leaves the 250,000 BTU/h load 7,700 BTU/h short. A site that sees -20°F needs the -20°F row.
5. Ignoring continuous loading. The table is for intermittent loading. Under continuous loading the guide multiplies the rates by 0.25, so the 300,100 BTU/h of the 500 gallon tank at 0°F becomes 75,025 BTU/h. A home rarely loads a tank that way, and a generator or a process heater can.
6. Letting the tank run dry, or leaving out appliances to come. With no reserve the 500 gallon tank lasts 36.6 days against 29.3 days with 20 percent kept back, and a late delivery then means a cold house. The guide also says to allow for appliances added later. A 80,000 BTU/h gas log on top of the default set takes the load to 330,000 BTU/h, over the 300,100 BTU/h that the 500 gallon tank gives at 0°F.

Common questions about propane tank size

Related calculators

• Gas pipe sizing calculator The pipe from the regulator to the appliances. Enter the connected load of this page in BTU/h.
• Furnace size calculator The furnace input that sets the largest line of the propane load.
• Tankless water heater size calculator A tankless unit is the biggest single input on many propane homes.
• Generator size calculator A standby generator on propane adds its own input and run hours.
• All tools Every public BuildSolver calculator in one list.

Used on the same job

• Boiler size calculator The boiler input for a hydronic home on propane.
• Combustion air calculator Combustion air openings for the propane appliances.
• Furnace gas input clocking calculator Check the input of a furnace from its gas meter, after the conversion to propane.