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Tank Volume Calculator

Calculators · Added

Total capacity is easy for any shape. The question worth a calculator is the second one: a dipstick reads a depth, and you want a volume. On a tank lying on its side those two are not proportional, and assuming they are can be twenty per cent out.

Cylinder on its side, with flat ends. Fuel and water tanks.

What a dipstick reads. Leave blank for a full tank.

Used for the weight figure only

How to use the tank volume calculator

  1. 1Choose the tank shape and the units your measurements are in.
  2. 2Enter the internal dimensions — diameter and length for a round tank.
  3. 3Enter the depth of liquid, or leave it blank for a full tank.
  4. 4Pick the contents if you want the weight as well as the volume.

Examples

A horizontal tank a quarter full by depth

Input
120 cm diameter, 240 cm long, 30 cm of liquid
Result
About 531 litres of a 2,714 litre capacity — 19.6%, not 25%

An upright drum

Input
60 cm diameter, 90 cm tall, filled to 45 cm
Result
127 litres, exactly half of the 254 litre capacity

About the tank volume calculator

The circular segment

The area of liquid in a horizontal cylinder is a circular segment, given by r²·arccos((r − h)/r) − (r − h)·√(2rh − h²) where r is the radius and h the depth. Multiply by the length and you have the volume.

It is not a formula anybody carries around, which is precisely why the mistake it prevents is so common: without it, the obvious thing to do is scale the capacity by the fraction of the depth, and that is wrong everywhere except the midpoint.

Making a dipstick chart

The table this produces at each tenth of the depth is the beginning of a calibration chart — read the depth, look up the volume. For a tank you check regularly it is worth marking the stick itself at the volumes that matter rather than at even distances, because those marks will not be evenly spaced.

On a cylindrical tank they bunch towards the top and bottom and spread out in the middle, which is the same curve seen from the other side: near the ends, a large change in depth is a small change in volume.

Frequently asked questions

Why is a horizontal tank not half full at half depth?
It is — that is the one point where depth and volume agree. Everywhere else they do not, because the wetted cross-section of a circle is a segment rather than a rectangle. A quarter of the depth covers about 19.6% of the area and three-quarters covers about 80.4%, and the curve between them is what makes a dipstick on a cylindrical tank so misleading.
What is a capsule tank?
A cylinder lying on its side with hemispherical ends rather than flat ones — the shape of a propane or LPG vessel. The two hemispheres together make one sphere, so the capacity is the cylinder plus a sphere of the same diameter, and the partial volume adds a spherical cap to the cylindrical segment.
Why does my answer differ from the tank's stated capacity?
Because this calculates an ideal shape from the dimensions you give it. A real tank has wall thickness, weld seams, internal baffles, a sump and often dished rather than flat ends, and the published capacity may be a usable figure that already excludes some of that. Where the number has to be right — a certification, a fuel reconciliation — the tank's own calibration chart is the authority.
Is the weight figure reliable?
It is the volume multiplied by the density you selected, which is arithmetic rather than an estimate. The densities offered are at roughly 15 to 20 °C and every one of them shifts with temperature — petrol by nearly one per cent per ten degrees. That matters for a stock reconciliation and not at all for checking what a stand has to carry.

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