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Water Tank Volume Calculator

Capacity and dip-level (partial fill) volume for vertical, horizontal and rectangular tanks.

Total tank capacity
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Total capacity
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Contents weight
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Horizontal cylindrical tanks don't fill linearly with dip height — the same rise in level represents more volume near the middle of the tank than near the top or bottom, because the circular cross-section is widest at the centreline. This tool uses the exact circular-segment formula, so the partial-volume figure is accurate at any fill height, not just a straight-line approximation.

How this is calculated

Vertical cylindrical and rectangular tanks fill linearly, so partial volume is simply the full cross-sectional area × fill height. Horizontal cylindrical tanks use the circular segment formula: V = L × [R² × cos⁻¹((R−h)/R) − (R−h) × √(2Rh − h²)], where R is the tank radius, h is the fill height measured from the bottom of the tank, and L is the tank length — this correctly accounts for the non-linear relationship between dip height and volume in a horizontal cylinder. Contents weight uses the selected fluid density; actual tank capacity may be slightly less than the calculated geometric volume once freeboard, internal fittings, and baffles are accounted for.