Propane Tank Volume calculator
Propane vessel volume with dished heads, gauge % and the 80% fill rule. Exact geometry, instant results, nothing leaves your browser.
Exact segment geometry — see methodology. Dished-head propane math is documented there too.
Residential propane vessels — 120, 250, 500 and 1000 gallon — are horizontal cylinders with dished (torispherical) heads, and they are governed by two conventions that confuse everyone: the tank size is its water capacity, and it is only ever filled to 80% to leave vapor space. So a "500 gallon" tank holds at most ~400 gallons of propane, and a gauge reading of 60% means 0.60 × 500 = 300 gallons.
This calculator models the dished heads explicitly (the method and its error bound are on the methodology page). Enter diameter and cylinder length, or jump straight to the pre-built 500-gal and 1000-gal charts where the geometry is already solved to nameplate capacity.
How this is calculated
V ≈ πr²Lcyl + 2·0.0809·D³V(h) ≈ seg(r,h)·Lcyl + (0.1545·D/r)·πh²(3r−h)/3Cylinder segment along the shell, plus dished heads scaled to match the ASME torispherical volume (error bounds on the formula page). See the full derivation, a worked example and a fill-ratio table on the asme f&d (torispherical) heads formula page.
FAQ
TVC-105/FAQHow many gallons are in my 500 gallon tank at 40% on the gauge?
0.40 × 500 = 200 gallons of propane. Float gauges read percent of water capacity directly.
Why can't a propane tank be filled to 100%?
Liquid propane expands strongly with temperature; the 20% vapor space prevents over-pressure. Delivery drivers fill to 80% by regulation.
What are typical 500 gallon tank dimensions?
Nominally about 37.5 in diameter and around 10 ft overall — but always trust the nameplate water capacity over tape-measure geometry.