Propane: gauges, fill rules and vessel math

Gauge % × water capacity = gallons, full means 80%, and the dished-head geometry behind every chart is measured against exact vessel math.

Propane is the tank people misread most, because the gauge shows percent of water capacity, not gallons — and “full” means 80%, never 100. Multiply the gauge percent by the tank’s water capacity and you have your gallons; the rest is knowing your daily burn so the number means something. The vessels themselves are dished-head cylinders whose end caps add a few percent over a plain cylinder, which our math accounts for exactly. Below: the calculator for any propane vessel, charts for the common sizes, the gauge-and-80%-rule explainer, and the clearance distances NFPA 58 requires when you site a tank.

Propane: gauges, fill rules and vessel math

Calculators

Propane vessel calculator (F&D heads)

Fill time

Charts

500 gal chart

1000 gal chart

250 gal chart

All propane charts

Guides

Reading the gauge & the 80% rule

How much propane is left

How long a tank lasts

Reference

500 gal dimensions + NFPA 58 clearances

What liquid propane weighs

F&D head formula & error bounds