What is liquid propane?

Figures checked Nov. 10, 2026

Liquid propane is propane stored as a liquid inside a tank or cylinder. A full tank is not all liquid; space is left for expansion: North Carolina's Department of Agriculture says a full tank is about 80% liquid. LP gas, short for liquefied petroleum gas, is the name you'll also see for propane.

Term	What it means
Liquid propane	propane as it sits in the tank
LP gas or LPG	liquefied petroleum gas; the US Department of Energy lists propane as “Propane (LPG)”
Full tank	about 80% liquid, leaving room for expansion

120 gal tankabout 96 gal usable
250 gal tankabout 200 gal usable
325 gal tankabout 260 gal usable
500 gal tankabout 400 gal usable
1,000 gal tankabout 800 gal usable

Tanks are filled to about 80% of their size, so the usable gallons are less than the size on the tank. Usable figures from propane suppliers' published charts.

Is propane a liquid or a gas?

In the tank, it is stored as a liquid, with space left over. North Carolina's Department of Agriculture says a full tank is about 80% liquid.

That space matters. Utah's State Fire Marshal says propane containers are filled to only 80% of their capacity, to allow for expansion.

LP gas vs propane

LP gas stands for liquefied petroleum gas. The US Department of Energy's fuel properties table lists propane as “Propane (LPG)”, giving the two names together.

On a tank, a bill or an appliance label, you'll see either one. If a label says an appliance is for LP gas, check with the maker or a certified propane technician before connecting it to anything, and use only the fuel the appliance is made for.

Why propane is sold by the gallon and the pound

Big tanks are sized in gallons and filled to about 80% of that. Utah's State Fire Marshal says DOT cylinders are filled by weight or by a fixed liquid level gauge. To turn pounds into gallons, a gallon weighs about 4.24 pounds by a propane retailer's figure.

A gallon of propane holds about 91,450 Btu of heat, by the US Energy Information Administration's figure. The propane weight page converts pounds and gallons.

What we don't cover here

We keep to what our sources say, so we don't cover the physics of how propane turns from liquid to gas, because we haven't checked an official source for it. Your propane supplier can explain how your own tank works.

Questions people ask

Is LP gas the same as propane?

LP gas means liquefied petroleum gas. The US Department of Energy lists propane as “Propane (LPG)”, giving the two names together.

Why is a propane tank not filled to the top?

To allow for expansion. Utah's State Fire Marshal says propane containers are filled to only 80% of their capacity.

Who should connect a propane appliance?

Have propane appliances installed and serviced by a certified propane technician.

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)

Sources for this page

3 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.
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.