Propane: tank sizes, run times and what's left

Figures checked Nov. 10, 2026

Cord & Tank's propane calculators work out how long a tank or cylinder will run your appliances, how much propane you have left, and how pounds turn into gallons. You type your own tank, gauge reading or appliance rating, and we do the sums with figures from named sources, shown on every page.

Question	Quick answer
How full is a full tank?	about 80% of its size
Gallons in a full 20-lb cylinder	about 4.7
Gallons in a full 500-gallon tank	about 400
Weight of a gallon of propane	about 4.24 lb

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.

Start with the sum you need

How long does a propane tank last? Your tank and your appliance's Btu rating give the hours and days.
Propane tank sizes: the gallons each size really holds when full.
How to check a propane tank level: read the gauge or weigh the cylinder, then turn it into gallons.
How much a gallon of propane weighs, with a pounds and gallons converter and the Btu in a gallon.
Does propane go bad? The date stamp rules for cylinders.
Where to store propane tanks: the official lines on garages, other buildings and vehicles.
What is liquid propane? LP gas and propane explained.

Tank and cylinder pages

Cylinders are sold by the pounds of propane they hold: 20 lb, 30 lb and 100 lb. Big tanks are sized in gallons: 120 gallon, 250 gallon, 325 gallon, 500 gallon and 1,000 gallon.

Each page has the calculator set to that size, so you only need to add your appliance.

The figures behind the sums

Heat: the US Energy Information Administration puts propane at about 91,450 Btu per gallon, and other official tables give 91,300. Our run times use the lower figure, so they err on the short side. Our cost sums use EIA's.

Fill: Utah's State Fire Marshal says propane containers are filled to only 80% of their capacity, to allow for expansion. Cylinders are filled by weight; their rated weight already allows for that fill, so it isn't taken off again.

Weight: about 4.24 pounds a gallon, from a propane retailer. We found no government figure, so we say so where we use it. Usable gallons for each tank size come from propane suppliers' published charts, and match the official fill rule.

What we don't do

We don't sell propane or tanks, and we don't give prices: type your own into the fuel cost comparer to compare propane with wood, oil or electric heat like for like, per million Btu.

We don't advise on installing tanks, lines or appliances. That is a job for a certified propane technician, and where a tank can sit is a question for your propane supplier or fire marshal.

Questions people ask

How long does a propane tank last?

It depends on the tank and the Btu rating of what it runs. Our calculator works it out from your figures and errs on the short side.

How many gallons are in a propane tank?

A big tank holds about 80% of its size when full. A full 20-lb cylinder holds about 4.7 gallons by propane suppliers' figures; exchange cylinders are often filled with about 15 lb.

Does propane go bad?

We found no official expiry date for propane itself. Cylinders have a requalification date stamped on them.

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

7 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: 91,452 Btu per gallon Official
From US EIA Monthly Energy Review, Sept 2026, Appendix A Table A1 (Approximate Heat Content of Petroleum and Biofuels), which says: “Propane 3.841” 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.
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.
Propane in a 20 lb exchange cylinder (net weight): 15 pounds of propane Other source
From Blue Rhino (exchange-cylinder maker): How much propane does Blue Rhino put in its tanks?, which says: “Blue Rhino propane grill tanks contain a net weight of 15 lbs. of propane.” Open the source (opens in a new tab)
Checked Nov. 9, 2026.
Gallons in a full 20 lb cylinder: 4.7 gallons Other source
From Ferrellgas (propane supplier): How to Choose the Right Propane Tank Size?, July 24 2025, which says: “20-lb: Holds up to 4.7 gallons 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: the two agreed.
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.
500-gallon propane tank: usable gallons at 80%: 400 gallons Other source
From Ferrellgas (propane supplier): How to Choose the Right Propane Tank Size?, July 24 2025, which says: “Holds 400 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, and its source label was corrected afterwards.