How much propane a 20 lb tank holds, and how long it lasts
Updated October 24, 2026
The “20 lb” on a grill cylinder is the weight of propane it holds when full. Propane weighs about 4.24 lb per gallon, so a full tank holds about 4.7 gallons. The steel tank itself weighs 17 to 18 lb empty; that figure is stamped on the collar as “TW” (tare weight).
Energy in the tank
A gallon of propane carries about 91,500 BTU. A full 20 lb tank therefore holds roughly 430,000 BTU. How long that lasts depends on the appliance.
| Appliance | Typical rating | Hours per full tank |
|---|---|---|
| Two-burner grill on high | 25,000 to 30,000 BTU/h | 14 to 17 |
| Four-burner grill on high | 40,000 to 50,000 BTU/h | 9 to 11 |
| Grill on medium | about half of high | roughly double the hours |
| Patio heater | 40,000 BTU/h | about 10 |
| Camp stove, one burner | 10,000 BTU/h | about 40 |
| Portable buddy heater, low | 4,000 BTU/h | about 100 |
Appliance ratings are the maximum draw. Most grilling runs below it, so a tank often outlasts the table.
Checking what is left
Tanks have no gauge of their own. Three ways to check:
- Weigh it. Subtract the tare weight stamped on the collar from the total; the remainder is propane. 10 lb of propane means half a tank.
- Pour warm water down the side. The steel below the propane level stays cold to the touch.
- Add an inline gauge between the tank valve and the regulator. They read pressure, not volume, so they are rough.
Exchange tanks hold less
Tanks from an exchange cage are usually filled to 15 lb rather than 20, which cuts the hours above by a quarter. The net weight is printed on the sleeve. See refill or exchange for how the prices compare.
Refilling
A refill station fills the tank by weight until it reaches 20 lb of propane, or until the overfill protection valve closes. Find one with the station finder.