Tank Volume Calculator
Pick your tank's orientation and head shape, enter its dimensions, and get total capacity plus fill volume instantly.
Worked examples
LPG storage vessel dipped to 1 m
A site technician checks how much propane is in a horizontal pressure vessel with standard 2:1 elliptical heads by reading the dipstick.
- D
- 2 m
- L
- 4 m
- h
- 1 m
≈ 7,330.4 L filled, of 14,660.8 L total capacity
Feed hopper tapering to a narrower outlet
A plant operator sizes a vertical mixing hopper that tapers from a 2 m base to a 1 m outlet, filled 2 m up its 3 m height.
- D-bottom
- 2 m
- D-top
- 1 m
- H / h
- 3 m / 2 m
≈ 4,421.5 L filled, of 5,497.8 L total capacity
How the formula works
Every horizontal shape here starts from the same picture: slice the tank's straight cylindrical shell at a right angle and you get a circle of radius r; liquid filled to height h cuts off a circular segment — the area below a horizontal chord. That chord sits a perpendicular distance r − h from the center, so the half-angle to its endpoints is acos((r−h)/r), and the segment's area follows directly from the full central angle θ. Multiply by the shell's length L and you have the wetted volume of the straight section.
Domed heads extend this the same way for every head style: a hemispherical, 2:1 elliptical, or custom head is just a sphere stretched (or compressed) along its axis by a depth-to-radius ratio a/R. That affine stretch scales the classic spherical-cap volume formula directly, which is why a sphere, a hemisphere-headed tank, and a 2:1-headed tank all resolve to one capped-ellipsoid formula with a as the only shape parameter — a=R gives a hemisphere, a=R/2 gives the 2:1 standard, and a=0 collapses it to a flat head worth zero volume. Vertical cone/frustum tanks use a different but equally direct idea: the radius tapers in a straight line from bottom to top, so stacking circular disks of that changing radius up to height h and integrating gives a closed-form cubic — no iteration needed. An oval (elliptical) cross-section is simply this same segment math with the circle stretched into an ellipse, scaling one axis by W/H.
Frequently asked questions
I don't know my tank's head shape — which option should I pick?
Check the tank's spec plate or purchase drawing first — pressure vessels almost always state the head type ("2:1 elliptical," "hemispherical," or "flat"). If you're measuring by hand, compare the head's bulge depth to its radius: a bulge of about a quarter of the radius is a 2:1 elliptical head (the ASME default for most process tanks), a bulge equal to the full radius is a hemispherical head (common on propane and pressure tanks), and a nearly flat end is a flat head (typical of basic cylindrical drums and IBCs). If it's somewhere in between, use "Custom ellipsoidal heads" and enter the measured bulge depth directly.
What's the difference between total capacity and filled volume?
Total capacity is how much the tank holds completely full, based only on its shape and dimensions — it's always calculated. Filled volume is how much liquid is inside right now, based on the fill height you measured. Leave the fill height field blank if you only want the tank's rated capacity; fill it in to also see the current volume and the fill percentage.
Why doesn't the diagram show the width (W) I entered for an oval tank?
The width of an elliptical cross-section is the tank's depth going into the page from this side view — the same reason you can't see a hallway's width by looking at it from one end. The diagram shows the two dimensions that define the profile you'd actually see standing beside the tank (length and cross-section height); width only becomes visible from an end-on view, which is why it still needs its own input even though the picture doesn't draw it.
How is a cone-bottom (frustum) tank different from a straight cylinder?
A frustum tapers linearly between two different diameters — a bottom diameter and a top diameter — over its height, so its cross-sectional area at the liquid surface changes with fill level even though the shape isn't curved. Set the top diameter to zero for a tank that comes to a sharp point (a true cone), or set it equal to the bottom diameter to get a plain straight-sided cylinder — the same taper formula reduces exactly to a regular cylinder's volume in that case, so there's no need to switch shapes.
Where should I measure the fill height from?
Always from the lowest interior point the liquid can reach, straight up to the liquid surface — for a horizontal tank that's the bottom of the round shell itself, not the top of the support saddles or legs it's resting on. For a cone-bottom or sphere-bottom vertical tank, that lowest point is the tip of the cone or the bottom of the sphere, not the top of any flat base plate underneath it.
My result differs slightly from another tank calculator online — why?
It's almost always a unit-conversion rounding difference, not a formula error. Some older tools use conversion factors rounded to 4-5 significant figures internally (for example, converting cubic feet to gallons at 7.4805 instead of the exact 7.480519...), which compounds into a few parts-per-million of drift on the final number. This calculator uses the exact NIST-defined conversion constants throughout, so if you need to match a legacy tool's output exactly, expect agreement to about 4 significant figures rather than every decimal place.