Estimate the liquid space inside a rectangular basin up to a chosen usable height. Subtract the space occupied by one vertical cylindrical tank, then optionally convert the remaining US gallons using your liquid density.

Formula: net ft³ = (inside length × width − π × tank outside radius²) × usable height; US gal = net ft³ × 1,728 ÷ 231

Worked example

A 20 × 15 ft inside basin at 1 ft usable height, with one 6 ft outside-diameter vertical tank, has about 271.73 ft³ of net geometric space, or about 2,032.65 US gal. At 8 lb/US gal, that is about 16,261 lb.

The tank occupies part of the basin

This model assumes one circular vertical tank footprint entirely inside a rectangular basin, with its outside wall reaching above the usable liquid height. If there are supports, other equipment or sloped walls, measure their displacement separately.

Use the height you actually allow

The chosen height is the liquid depth available after any freeboard or other allowances have been set elsewhere. Rainfall, connected piping, wall openings and impermeability are not modeled. EPA SPCC guidance discusses containment requirements, but this geometric result is not a compliance determination.

Weight needs an explicit liquid density

US gallons and pounds cannot be interchanged without the actual liquid density at suitable conditions. The optional pounds output multiplies geometric gallons by your entered lb/US gal; omit density if only capacity is needed.

Explore the related calculation

For a different starting point, try the tank fill from weight calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

Found a problem? Email contact@gallonstopounds.org.

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