How many gallons of propane are in a 20-lb tank?

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.

Exchange or refill?

If you have your cylinder refilled at a propane dealer, it is filled by weight up to its rated 20 lb. That rated weight already allows for the 80% fill, so 80% isn't taken off again.

Exchange cylinders are a different story. One exchange brand, Blue Rhino, says its grill tanks contain a net weight of 15 pounds of propane. The federal weights and measures office (NIST) says most 20-lb cylinders are filled and labeled to that same net weight.

Our calculator asks which you have. If you're not sure, it works on the lower exchange fill and says so. Check the net weight on the label to be sure.

Searching for a twenty-gallon propane tank?

If you mean the grill tank, that's the 20-lb cylinder: cylinders are named by pounds of propane, not gallons. If your tank really is sized in gallons, check its data plate and ask your propane supplier.

A consumer protection column from Bucks County, Pennsylvania, also called the grill tank a twenty-gallon tank, saying it holds about five gallons when full.

How long does a 20-lb propane tank last?

It depends on the Btu rating of what you run. Find it on the appliance's rating plate, type it into the calculator above, and add the hours a day you use it.

We use 91,300 Btu per gallon for run times, the lowest official figure we hold, and work at the full rating. Results are rounded down, so they err on the short side.

How to tell how much is left

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

We don't list sizes or empty weights, because they vary by maker. Use the TW stamp on your own cylinder.

The date stamp and the OPD

The cylinder itself has a time limit. 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.

Cylinders from four to forty pounds also need an overfilling prevention device (OPD). Utah's State Fire Marshal says cylinders without an OPD cannot be refilled. The rule comes from a national fire code written by the National Fire Protection Association (NFPA), which many states have adopted as state law. More on both in does propane go bad?

Where to keep it

Keep the cylinder outdoors, and use outdoor-only grills and heaters outdoors. See where to store propane tanks for the official lines.

Questions people ask