How to Measure a Tank When You Don't Know What It Is

Every chart and calculator needs the same three facts: the shape, the inside dimensions, and the orientation. Here's how to get them off an unlabeled tank.

Shape first. Run a hand along the side. Fully curved top to bottom: cylinder (or true oval). Flat vertical band between curved top and bottom: obround — the standard oil-tank profile. Flat everything: rectangular. For a horizontal cylinder, also feel the ends: flat ends are a plain cylinder; bulged ends mean dished heads, which add a few percent.

Then dimensions. Outside measurements minus twice the wall are close enough for steel (walls are thin); for thick-walled poly tanks measure inside through the lid where possible. For a buried tank, interior stick depth equals the diameter, and a before/after metered delivery pins down the length — the technique is in measuring underground tanks.

Sanity-check against standards. Most tanks are standard sizes: 27×44 obround sections, 48 or 64-inch underground diameters, 22.5-inch drums. Compare your numbers to the sizes library — matching a standard means a ready-made chart; not matching means the universal calculator with your measured dimensions, which is exactly what it's for.