How this instrument works
A swimming pool's capacity comes down to one of two simple shapes for most residential installs: a rectangular box, or a round cylinder standing on its side (the common shape for above-ground pools). Both follow ordinary volume geometry — length times width times depth for a rectangle, or pi times radius squared times depth for a circle — and this instrument computes whichever one matches the pool you've selected.
Pick 'Rectangular' and it multiplies length, width and average depth directly. Pick 'Round / circular' and the Length field is read as the pool's diameter instead, with Width ignored, and the volume comes from pi times (diameter ÷ 2) squared times average depth — the standard cylinder formula. Either way, the resulting cubic-foot volume is multiplied by 7.48052, the exact number of US gallons in one cubic foot, to return the answer in the unit pool chemicals, fill times and pump ratings are actually specified in.
'Average depth' is doing real work in both formulas — an in-ground pool with a shallow end and a deep end doesn't have one single depth, so blending a representative average across the pool (rather than using either extreme) is what keeps the volume figure realistic. A pool's true gallon count matters directly for chemical dosing (chlorine, pH adjusters and algaecides are all dosed per gallon), for estimating how long a garden hose or fill line will take to top it off, and for confirming a pump and filter are rated for the pool's actual water volume.
- Select Pool shape — Rectangular or Round / circular.
- Enter Length (ft) — the pool's length, or its diameter if round.
- Enter Width (ft) — the pool's width; this field is ignored for a round pool.
- Enter Average depth (ft) — blend shallow-end and deep-end measurements into one representative figure rather than using either extreme alone.
- Read Volume (US gallons) beneath the inputs — it recalculates instantly as any field or the shape selection changes.
Worked example — a 32 × 16 ft rectangular in-ground pool
Select Rectangular, enter 32 into Length (ft), 16 into Width (ft), and 5 into Average depth (ft) — a mid-size in-ground pool blending a shallower and deeper end. Volume works out to 32 × 16 × 5 = 2,560 ft³.
Volume (US gallons) reads 19,150.1 — that figure being 2,560 multiplied by 7.48052, the exact gallons-per-cubic-foot conversion. A realistic number for a residential in-ground pool of this size, and a reasonable starting figure for chlorine dosing charts or estimating a fill time from a garden hose's known flow rate.
Questions
What counts as a pool's 'average depth'?
A single representative figure blending the shallow and deep ends rather than using either extreme — many pool suppliers and dealers list an average-depth figure directly on the pool's spec sheet, or you can estimate it by averaging a shallow-end and deep-end measurement. Using only the deep-end number overstates the pool's true volume, while using only the shallow end understates it.
How does the round pool formula differ from the rectangular one?
A round pool's Length field is read as its diameter, and Width is ignored, since a circle needs only one dimension besides depth. The volume then comes from the standard cylinder formula, pi times the radius (diameter divided by two) squared times average depth, rather than the simple length-times-width multiplication used for a rectangular pool.
How is this different from the site's Round Pool Volume instrument?
This calculator handles both rectangular and round pools behind one shape selector, matching how most residential pool-volume questions actually get asked. The dedicated round pool volume instrument is scoped specifically to round above-ground pools only, with diameter and average depth as its only two inputs — a simpler, single-purpose version of this same cylinder math for anyone who only needs that one case.
Does this work for oval, kidney-shaped or freeform pools?
Not directly — those shapes need to be approximated by breaking them into rectangular and/or circular sections, calculating each separately, and summing the results, or estimated by treating the pool as the nearest rectangle or oval-as-ellipse and adjusting downward slightly, since this instrument's two formulas only cover a clean rectangle or a true circle.
Why multiply by 7.48052 instead of some other gallon conversion?
Because 7.48052 is the exact number of US gallons in one cubic foot, following directly from the US gallon's legal definition as 231 cubic inches — not a rounded or approximate figure. Once the pool's volume is computed in cubic feet from its dimensions, this single multiplication converts it precisely to gallons.