Capsule tank volume calculator
A horizontal cylinder with a hemisphere on each end. Enter the inside diameter and the straight shell length, then a dipstick reading, for gallons, litres and Imperial gallons at that depth.
Exact segment geometry — see methodology. Dished-head propane math is documented there too.
What to measure
Measuring a capsule tank
Enter the inside diameter and the straight shell length — seam to seam, not end to end. Each hemispherical end is half a diameter deep, so the overall length is the shell length plus one full diameter. If the tank's plate gives only the overall length, subtract the diameter before entering it.
V = πr²·L + (4/3)πr³V(h) = seg(r,h)·L + πh²(3r−h)/3The ends together form one sphere, so the head term is the textbook spherical cap — exact, with no approximation. Worked example: a 48 in diameter, 96 in shell holds 1,002.7 US gal full. At an 18 in dipstick reading it holds 336.9 gal, of which 79.3 gal sits in the two ends. Derivation and a fill-ratio table: capsule tank formula.
How much the rounded ends add
The ends are worth surprisingly little shell. On every diameter, the two hemispheres hold the same as two-thirds of a diameter of straight shell — so a capsule holds exactly what a flat-ended cylinder ⅔·D longer would hold when full. Partly full, the ends hold a smaller share near the bottom and top.
| Diameter | Both ends together | Shell, per inch of length | Ends = this much extra shell |
|---|---|---|---|
| 24 in | 31.3 gal | 1.96 gal | 16.0 in |
| 30 in | 61.2 gal | 3.06 gal | 20.0 in |
| 36 in | 105.8 gal | 4.41 gal | 24.0 in |
| 42 in | 167.9 gal | 6.00 gal | 28.0 in |
| 48 in | 250.7 gal | 7.83 gal | 32.0 in |
| 60 in | 489.6 gal | 12.24 gal | 40.0 in |
| 72 in | 846.0 gal | 17.63 gal | 48.0 in |
| 84 in | 1,343.5 gal | 23.99 gal | 56.0 in |
| 96 in | 2,005.4 gal | 31.33 gal | 64.0 in |
| 120 in | 3,916.8 gal | 48.96 gal | 80.0 in |
Ends dished rather than hemispherical — 2:1 elliptical or ASME flanged-and-dished? Use the dished head tank calculator. Propane tanks have their own page: propane tank volume.
FAQ
TVC-114/FAQWhat is a capsule tank?
A horizontal cylinder closed at each end by a hemisphere — a half-sphere the same diameter as the shell. The two ends together make one complete sphere, which is why the formula is simply a cylinder plus a sphere.
Which length do I enter?
The straight shell only, from the seam at one end to the seam at the other. If you only have the overall length, subtract one diameter: each hemispherical end is half a diameter deep.
How do I calculate the volume of a capsule tank?
Total: π × r² × L + 4⁄3 × π × r³, with r the inside radius and L the straight shell length, then ÷ 231 for US gallons. A 48 in × 96 in shell holds 1,002.7 gal.
How many gallons are in a partly full capsule tank?
Add the circular segment of the shell (segment area × shell length) to a spherical cap of the same depth: πh²(3r − h) ÷ 3. Set the dipstick reading in the calculator above. At 18 in on the 48 in example tank it holds 336.9 gal.
Does this work for an upright capsule?
Yes. Select Capsule V above and enter the diameter and the straight wall height. The total capacity is the same as a horizontal capsule of the same size, but the gallons at each depth are different.
Sources and standards
- Methodology — partial-fill formulas, head approximations and their tested errortankvolumecalc.comhttps://tankvolumecalc.com/methodology/
- Handbook 44, Appendix C — General Tables of Units of MeasurementNational Institute of Standards and Technology, U.S. Department of Commercehttps://www.nist.gov/document/2026-nist-handbook-44-appendix-cUS gallon = 231 in³ exactly; Imperial gallon = 4.54609 L.
Every linked source above was retrieved and checked on 2026-11-01.