Heating Oil Tank Volume calculator
Exact obround math for 275 and 330 gallon heating oil tanks. Exact geometry, instant results, nothing leaves your browser.
Exact segment geometry — see methodology. Dished-head propane math is documented there too.
The standard 275 and 330 gallon home heating oil tanks are obround: flat vertical sides with a semicircular top and bottom. Most online calculators model them as ellipses, which under-reads the middle of the tank by several percent. This calculator uses the true obround profile — a circular segment through the rounded zones and straight-walled math in between — and matches manufacturer gauge chart books to within a couple of percent at every inch.
The default dimensions are the standard vertical 275 (27 in wide × 44 in tall × 60 in long). A 330 is the same section, 72 in long. For a tank lying flat, use the universal calculator with the Oil Tank H shape. Typical practice fills a 275 to about 250 gallons to leave expansion room — so a "full" gauge is not the brim-full geometric number.
How this is calculated
V = (πR² + W·S)·L, R=W/2, S=Ht−Wh≤R: A=seg(R,h) | R<h≤R+S: A=½πR²+W(h−R) | h>R+S: A=πR²+WS−seg(R,Ht−h)Solved piecewise — circular segment through the domed bottom, linear through the straight middle, total-minus-segment through the top dome. See the full derivation, a worked example and a fill-ratio table on the obround tank (275/330 oil profile) formula page.
FAQ
TVC-104/FAQHow much oil is left at 12 inches on a 275 vertical tank?
About 119–120 gallons. Set the fill slider to 12 in or read it straight off the 275V chart.
Why does my tank chart say 94 gallons at 16 inches but an ellipse calculator says less?
Because the tank is obround, not elliptical — the flat sides hold more oil per inch through the middle of the tank. Our math matches the manufacturer chart.
How big is a 330 gallon tank?
Same 27 × 44 in section as a 275, but 72 in long instead of 60 in.