Weigh it — don't guess

The only reliable way is to weigh the tank.

Propane tanks have a tare weight (TW) stamped on the collar — that’s the empty tank weight. A full 20lb BBQ tank usually weighs about 36-38 lbs total. Put it on a bathroom scale, subtract the TW, and you know exactly how many pounds of propane are left.

The built-in float gauges on most tank valves are notoriously inaccurate. They lie. The hot water trick (pour warm water down the side and feel for the cold line) works in a pinch, but it’s finicky and temperature-dependent.

If you’re out camping or don’t have a scale, the hot water trick is better than nothing. Otherwise, buy a cheap luggage scale and weigh it before every trip.

Trust the scale, not the gauge.