How do I calculate the volume of a cylindrical tank?

Multiply the circle area of the end by the tank length. For a vertical tank that end is the base and the length is the height; for a horizontal tank the end is the circular face and the length runs along the ground. A tank 4 feet across and 6 feet long holds about 564 gallons. This tool does both orientations in gallons and litres.

How do I work out a part-full horizontal tank?

A lying-down cylinder is the hard one, because the fluid makes a circular segment, not a neat fraction of the circle. Enter a fill depth and the tool uses the segment-area formula to find exactly how much is in there — that is why a horizontal tank half full by depth really is half full, but a third full by depth is not a third of the volume.

Does this handle tank ends and dished heads?

No — it treats the tank as a plain cylinder. Real tanks often have domed or dished ends that add a little capacity, and a stand or sump changes the usable amount. Take the cylinder figure as the body volume and add or trust the maker for the ends.

Tank volume calculator

This models the tank as a plain cylinder. Dished ends, internal baffles, a sloped base or a standpipe all shift the true capacity, so use the figure for planning a fill or a haul and trust the tank's own gauge for anything that must be exact.

Pick whether the tank stands up or lies on its side, enter the diameter and the length, and read the full volume in gallons and litres. Add a fill depth and the tool works out how much is actually in a part-full tank — the tricky case when it is lying down.

Worked example

A tank 4 ft across is π × 2² ≈ 12.57 sq ft on the end. Six feet long that is 75.4 cubic feet, about 564 gallons or 2135 litres. Lay it down and fill it to 1 foot deep and the segment maths gives roughly 110 gallons — under a fifth, because the bottom of a round tank is narrow.

The formula

full = π × (D ÷ 2)² × L · segment = [r²·acos((r−h)/r) − (r−h)·√(2rh − h²)] × L

The full volume is the end circle times the length either way up. A part-full horizontal tank holds a circular segment of fluid, so the second formula finds that segment's cross-section from the fill depth h and radius r, then multiplies by the length. A vertical tank is easier — the fill is just a shorter cylinder.

Questions

How do I calculate the volume of a cylindrical tank?: Multiply the circle area of the end by the tank length. For a vertical tank that end is the base and the length is the height; for a horizontal tank the end is the circular face and the length runs along the ground. A tank 4 feet across and 6 feet long holds about 564 gallons. This tool does both orientations in gallons and litres.
How do I work out a part-full horizontal tank?: A lying-down cylinder is the hard one, because the fluid makes a circular segment, not a neat fraction of the circle. Enter a fill depth and the tool uses the segment-area formula to find exactly how much is in there — that is why a horizontal tank half full by depth really is half full, but a third full by depth is not a third of the volume.
Does this handle tank ends and dished heads?: No — it treats the tank as a plain cylinder. Real tanks often have domed or dished ends that add a little capacity, and a stand or sump changes the usable amount. Take the cylinder figure as the body volume and add or trust the maker for the ends.

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