How Much Propane Is Left in My Tank?

One multiplication answers it: gauge percent × water capacity = gallons of propane. A 500-gallon tank reading 38% holds 190 gallons; a 250 at 60% holds 150. The gauge reads percent of water capacity, and that's the whole conversion.

"Full" is 80%, not 100 — the vapor space is mandatory expansion room. So after a delivery a 500 shows about 80% (400 gallons), and the practical working range of the tank is 400 gallons down to your reorder point.

When to reorder: most suppliers say 20–30%. On a 500 that's 100–150 gallons, which sounds comfortable until a cold snap — a furnace drawing hard can burn 5–8 gallons a day in a heated home. Below 10–15% you risk pressure problems in deep cold and an out-of-gas call, which usually requires a paid leak check before relighting.

Gauges are ±5% instruments. If a reading drives a real decision, cross-check it against your delivery ticket history or watch the gauge across a week of known usage. The geometry behind every reading is on our propane chart pages.