Last updated: 2026-06-19

Propane Tank Duration

How long a propane tank lasts comes down to two numbers: how much energy the tank holds, and how fast the appliance burns it. Divide the first by the second and you get the runtime. Both are expressed in BTU (British Thermal Units), the standard unit for fuel energy and appliance output.

The energy ÷ rate method

A full tank holds a fixed amount of energy. An appliance consumes energy at its rated output, measured in BTU per hour. Runtime is simply the tank's energy divided by that rate:

The energy content of a tank comes from the propane it holds. Propane carries about 21,600 BTU per pound, so a tank's nominal size in pounds translates directly into BTU. A 20 lb tank holds roughly 430,000 BTU; a 30 lb tank about 649,000 BTU; a 40 lb tank about 860,000 BTU; and a 100 lb tank about 2,160,000 BTU.

Worked example

A standard 20 lb grill tank feeding a grill rated at 30,000 BTU per hour:

So a single 20 lb tank covers roughly fourteen hours of grilling at full heat — many weekend cookouts before a refill. Step up to a 100 lb tank on the same grill and the runtime stretches to about 72 hours.

Why real runtime is usually longer

This calculation assumes the appliance runs flat out, every burner on high, for the entire time. Most cooking happens at medium heat or with some burners off, so in practice a tank lasts well beyond the full-output estimate. Treat the result as a conservative floor rather than an exact prediction.

Two factors can push the other way. Cold weather lowers the rate at which liquid propane vaporizes inside the tank, which can starve a high-demand appliance and reduce its effective output. And a tank that was not filled completely, or an aging regulator, will fall short of the nominal figure. For sizing a heating appliance to a space rather than estimating fuel duration, see the Air Conditioner BTU Sizing Calculator.