Propane Tank Runtime Calculator: How Long a 20 lb Tank Lasts

Runtime on a full 20 lb tank and a 1 lb cylinder. Most cooking happens at roughly half throttle; heaters usually run on high.

The formula is hours = pounds of propane x 21,548 / (rated BTU per hour x throttle fraction). A 4-burner grill rated at 48,000 BTU running at about half its output uses 24,000 BTU an hour, so a full 20 lb tank lasts 431,000 / 24,000, about 18 hours of cooking. At 45 minutes per cook, that is roughly 24 cooks per tank.

The rated BTU is the total for all main burners on high. Side burners and sear burners add to it only when they are lit. Cold weather lowers the pressure a tank can deliver and wind pulls heat off the cooking surface, so real consumption in winter can be noticeably higher than the formula. A partly used tank holds less: weigh it and subtract the tare weight stamped on the collar to know what is left.

Weighing is the most reliable method. Subtract the tare weight stamped on the collar (usually around 17 lb for a 20 lb tank) from the current weight to get pounds of propane remaining. A hanging or platform scale such as the Flame King Digital Propane Tank Scale ($15.38) reads it directly. Inline pressure gauges are less precise, because propane pressure depends on temperature rather than fill level until the tank is nearly empty. The warm-water trick, pouring warm water down the side and feeling for the cool line, gives a rough level without tools. Keeping a spare full tank, such as the Flame King YSN230 20 lb Propane Tank with Gauge, is the simplest fix for running out mid-cook.

A 20 lb tank is far cheaper per BTU. Disposable 1 lb cylinders cost several times more per pound of propane than a refilled 20 lb tank, and even more than a tank exchange. For tabletop griddles and portable heaters used at home, an adapter hose such as the Gas One 4 ft. 1 lb to 20 lb Propane Adapter Hose lets the appliance run from a 20 lb tank, provided the appliance manufacturer allows it. Refilling at a station is usually cheaper than exchanging, because exchange tanks are often filled to 15 lb rather than 20.

Fuel use follows the BTU you actually need, not the biggest number on the box. A well-built grill with good heat retention, like the Weber Genesis E-325 Gas Grill (Propane), cooks at lower burner settings than a thin budget grill with higher rated BTU. A 36 inch griddle such as the Blackstone 36 in. Original Griddle with Built-in Hood only burns fuel on the zones you light. For patios, a 46,000 BTU mushroom heater like the Amazon Basics 46,000 BTU Propane Patio Heater with Wheels empties a 20 lb tank in about 9 hours, while an electric infrared heater such as the Bromic Tungsten Smart-Heat 4000W Electric Patio Heater avoids tank swaps entirely where you have the circuit. See the best gas grills, the best griddles and the propane burn time chart.