Round tank gallons calculator

Type the diameter and the water depth. You get the gallons and every step of the math.

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Answer: 95,123 gal

Area of the floor = 0.785 × diameter × diameter: 0.785 × 30 ft × 30 ft = 706.5 ft².
Volume = area × water depth: 706.5 ft² × 18 ft = 12,717 ft³.
In gallons: 12,717 ft³ × 7.48 gal/ft³ ≈ 95,123 gal.

Exam-practice math only. It is not an instruction for a real plant, well or tank: for that, follow your system's procedures and ask your supervisor.

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The formula

The volume of a tank, round or rectangular, is its floor area × the depth, in cubic feet; cubic feet × 7.48 gives gallons. A rectangle's area is length × width.[1]

Sources

US EPA Region 6, NPDES Reporting Requirements Handbook, XIII.A Math Formulas, 1. Length X Width = Area; 3. Surface Area X Depth = Volume (clarifier, pond, pipe); 4. Volume in cu. ft. X 7.48 = gallons (pages 29-30) (read November 13, 2026)

Reviewed November 13, 2026. Published by OperadorListo. The sources above are the authority. This is a summary in our own words: check the source before you act on it.