How many gallons of propane are in a 100-lb tank?

Figures checked Nov. 10, 2026

A full 100-lb propane cylinder holds about 23 gallons, by propane suppliers' published figures. Our calculator divides the weight by about 4.24 pounds a gallon, so it shows a touch more than that round figure.

100-lb cylinder	Propane inside
Filled to its full rated weight	about 23 gallons
Weight of a gallon of propane	about 4.24 lb

20 lb

4.7 gal

30 lb

7 gal

100 lb

23 gal

Gallons each cylinder holds when filled to its rated weight, from propane suppliers' published figures.

How long your propane will last

The sums behind this tool are checked against 4 run times printed by a heater maker (ours must come out at or below them), and 31 checks in all, including the limits where it gives no number.

A cylinder sold by weight

The 100 lb rating is the weight of propane the cylinder holds when full. Its rated weight already allows for the 80% fill, so 80% isn't taken off again.

The weight of a gallon comes from a propane retailer; we found no government figure. See propane weight per gallon for the details.

How long does a 100-lb propane tank last?

That depends on what it runs. Take the Btu rating from each appliance's rating plate, type it into the calculator above, and add the hours a day.

Run times use 91,300 Btu per gallon, the lowest official figure we hold, at the full rating, rounded down. So the answer errs on the short side.

How to check what's left

Weigh the cylinder and take off its TW (tare weight) stamp, the empty weight. The difference is the propane left, in pounds. The propane tank level page turns it into gallons.

Sizes and empty weights vary by maker, so we don't list them. Use the TW stamp on your own cylinder.

Date stamp, hookups and storage

Utah's State Fire Marshal: All DOT cylinders must be recertified 12 years after manufacture date and every 5 years there after. Ask your supplier to check the date stamp. Utah's State Fire Marshal says cylinders that are out of qualification must not be refilled.

If the cylinder feeds a home appliance, have the hookup installed and serviced by a certified propane technician. Keep cylinders outdoors: see where to store propane tanks.

Questions people ask

How many gallons are in a 100-lb propane tank?

About 23 gallons when filled to its full rated weight, by propane suppliers' figures.

Why does the calculator show a little more than the chart?

It divides the weight by about 4.24 pounds a gallon and rounds down to a tenth, while the suppliers' figure is a round number.

How long will a 100-lb tank run a heater?

Type the heater's Btu rating from its rating plate into the calculator, with the hours a day you use it.

Before you light it

Carbon monoxide (CO) can kill. US Consumer Product Safety Commission (Official): “Fuel-burning heating systems, including furnaces and fireplaces, can produce CO, an odorless, colorless and deadly gas.” Source(opens in a new tab)
Fit CO alarms and test them. US Consumer Product Safety Commission (Official): “CO alarms should be placed on every level of the home and outside sleeping areas.” “Test the alarms every month to make sure they are working.” Source(opens in a new tab)
Have appliances checked every year. US Centers for Disease Control and Prevention (Official): “Have your heating system, water heater and any other gas, oil, or coal burning appliances serviced by a qualified technician every year.” Source(opens in a new tab)
Chimneys and vents too. US Fire Administration (Official): “Have chimneys and vents cleaned and inspected at least once a year.” Source(opens in a new tab)
If a CO alarm sounds (US: call 911): US Centers for Disease Control and Prevention (Official): “If the detector sounds leave your home immediately and call 911.” Source(opens in a new tab)
Know the signs. US Centers for Disease Control and Prevention (Official): “The most common symptoms of CO poisoning are headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion.” Source(opens in a new tab)
Carbon monoxide (CO). CPSC (Official): "Fuel-burning heating systems, including furnaces and fireplaces, can produce CO, an odorless, colorless and deadly gas." "CO alarms should be placed on every level of the home and outside sleeping areas." Source(opens in a new tab)
If you smell gas (US: call 911). Connecticut Public Utilities Regulatory Authority (Official): "If the smell is strong or you are unsure, leave the building and then call." "Go to a phone that is not near the smell and call your propane company right away." "Don't smoke or strike any matches." "Don't flip light switches on or off." "Put out all open flames." "Call your propane company or 911 for help." This is general advice from one state's regulator: follow your own propane supplier's emergency instructions too. Source(opens in a new tab)
Keep propane cylinders outdoors. Utah State Fire Marshal (Official): "Never store a cylinder inside a house, building, or a garage." Source(opens in a new tab)
Outdoor-only heaters, grills and stoves stay outdoors. Mississippi State University Extension (Official), on outdoor-use-only heaters: "Never use them inside, even temporarily." Source(opens in a new tab)

Sources for this page

5 figures, each with its source

Every figure on this page, with its source. Open one to see the exact words on the source page and how it was checked.

Heat content of propane, for run times only (lowest official figure, kept as a safety margin): 91,300 Btu per gallon Official
From USDA Forest Service, Forest Products Laboratory: Fuel Value Calculator (updated July 2004), hosted by Nebraska Energy Office, which says: “Propane | gallon | 91,300 | 71,900 | 79%” Open the source (opens in a new tab)
Checked Nov. 10, 2026.
Gallons in a full 100 lb cylinder: 23 gallons Other source
From Ferrellgas (propane supplier): How to Choose the Right Propane Tank Size?, July 24 2025, which says: “100-lb: Holds 23 gallons of propane.” Open the source (opens in a new tab)
Checked Nov. 9, 2026. A second check re-opened the source page and matched it on Nov. 9, 2026.
DOT propane cylinder requalification: first due 12 years after the manufacture date, then every 5 years (date stamped on the collar; ask your supplier to check it) Official
From Utah State Fire Marshal: LP-Gas Basic Filling Procedures, which says: “All DOT cylinders must be recertified 12 years after manufacture date and every 5 years there after.” Open the source (opens in a new tab)
Checked Nov. 10, 2026. A blind check looked it up again on Nov. 10, 2026 without seeing our figure: it found that our figure or its wording needed correcting, and the corrected version is the one shown.
Weight of a gallon of propane: 4.24 pounds per gallon Other source
From U-Haul (retailer): 20-lb Steel Propane Tank product page (answer in the page's customer Q&A, 2021), which says: “The Propane that should be going into this tank only would weigh about 4.24lbs per gallon of propane.” Open the source (opens in a new tab)
Checked Nov. 10, 2026. A second check re-opened the source page and matched it on Nov. 9, 2026. A blind check looked it up again on Nov. 10, 2026 without seeing our figure: it didn't find a better source, so this figure stands.
Maximum fill of a propane tank: 80% Official
From Utah State Fire Marshal: LP-Gas Basic Filling Procedures, which says: “To allow for expansion, propane containers are to be filled only to 80% of their capacity.” Open the source (opens in a new tab)
Checked Nov. 9, 2026. A second check re-opened the source page and matched it on Nov. 9, 2026. A blind check looked it up again on Nov. 10, 2026 without seeing our figure: the two agreed.