Tank Volume Calculator
Partial-fill volume of a horizontal cylinder (flat, elliptical or hemispherical heads), vertical, rectangular or cone-bottom tank from the dipstick depth.
Litres, m³, US and UK gallons in the tank and at the measured depth, the fill percentage, the head volume, and a depth-by-depth chart to print for the dipstick.
Example: A 100 cm × 200 cm horizontal cylinder holds 1 571 L; at 25 cm on the dipstick it holds 307 L (19.6 %), at 50 cm 785 L; 2:1 elliptical heads on a 2 m tank add 2 094 L.
Geometry only —
the tank as drawn.
How each shape is filled, what the heads add, and what real tanks do differently.
Horizontal cylinder
The liquid cross-section at depth h in a circle of radius r is the circular segment r²·acos((r − h)/r) − (r − h)·√(2rh − h²); multiplied by the length it gives the partial volume, and at h = 2r it is the full circle. This is why a horizontal tank is not linear on the dipstick: the first and last quarters of the depth hold much less than the middle half.
Heads, vertical and cone tanks
Hemispherical heads together make a sphere, filled to depth h as a spherical cap πh²(3r − h)/3; 2:1 elliptical heads are that spheroid squashed to half the axial depth, so their volume is half the sphere's at every level. Vertical cylinders and rectangular tanks fill linearly; a cone-bottom tank fills as a cone (radius growing with height) until the cylinder starts. Dished-head knuckles, which real pressure-vessel heads have, are not modelled.
Reading the numbers
Volumes are nominal — inside dimensions with no wall thickness, fittings, sump or baffles — so a real tank holds a little less and a calibrated chart from the maker beats this one. Unit factors: 1 m³ = 1 000 L = 264.172 US gallons = 219.969 imperial gallons. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Circular segment r² acos((r − h)/r) − (r − h)√(2rh − h²) × length; spherical-cap volume for hemispherical heads, halved for 2:1 elliptical heads; cone by similar triangles; 1 m³ = 264.172 US gal
Last reviewed 22 September 2026. How results are checked: How we verify.