For a rectangular pool whose bottom slopes evenly along its full length, enter inside length and width, shallow and deep water depths, and the water density to estimate filled volume and weight.

Formula: average depth = (shallow + deep) ÷ 2 for one straight slope; ft³ = length × width × average depth; US gal = ft³ × 1,728 ÷ 231; lb = US gal × entered lb/US gal

Worked example

A 30 × 15 ft rectangular pool with a continuous slope from 3 to 8 ft has a 5.5 ft average depth and contains 2,475 ft³, or about 18,514.29 US gal. At an entered 8.33 lb/US gal, the water weighs about 154,224 lb.

This model requires one continuous slope

A flat shallow shelf, diving well, benches, steps or a curved wall changes the volume. Split those shapes into measured sections rather than forcing them into one average. Length and width are water-surface interior dimensions.

The gallon is the US liquid gallon

NIST defines it as exactly 231 in³. Imperial gallons are larger and must not be substituted. The calculated weight uses the density supplied in pounds per US gallon.

Water density changes

USGS notes that temperature and dissolved substances affect water density. The example’s 8.33 lb/US gal is illustrative; use a representative value if the weight matters. This is an inventory estimate, not structural load approval or a fill recommendation.

Explore the related calculation

For a different starting point, try the water 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.

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