Pool Volume Calculator

Pick your pool shape, enter its dimensions and the shallow and deep end depths, and get the gallons it takes to fill — plus liters, hose fill time, and estimated water cost.

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How pool volume is calculated

A pool is just a container: surface area × average depth gives cubic feet, and each cubic foot holds 7.48 gallons. The clever bit is average depth. Most pools slope from a shallow end to a deep end, and as long as that slope is reasonably steady, the pool holds exactly as much water as a flat-bottomed pool at the midpoint depth — so (shallow + deep) ÷ 2 does the job. A 3 ft shallow end and 8 ft deep end average 5.5 ft. If your pool is one depth everywhere (most above-ground pools), enter that depth in both fields.

The formulas

Rectangle: L × W × avg depth   ·   Round: π/4 × d² × depth   ·   Oval: 0.89 × L × W × avg depth   ·   Gallons = cu ft × 7.48

All dimensions are in feet, giving volume in cubic feet; multiplying by 7.48 converts to US gallons (and by 28.32 to liters). For a round pool, d is the diameter — the full distance across. The oval factor 0.89 is the pool-industry standard: real oval pools are closer to a rectangle with rounded ends than a true ellipse (which would be 0.785), so they hold a little more than the ellipse formula predicts.

Worked example

A 16 × 32 ft rectangular pool with a 3 ft shallow end and 8 ft deep end: average depth = (3 + 8) ÷ 2 = 5.5 ft, so volume = 16 × 32 × 5.5 = 2,816 cubic feet = 2,816 × 7.48 ≈ 21,064 gallons (about 79,740 liters).

Filling with a 9 GPM garden hose takes 21,064 ÷ 9 ÷ 60 ≈ 39 hours — about a day and a half. At $6.50 per 1,000 gallons, the water costs roughly $137.

Set expectations before you turn on the hose

First-time pool owners are usually surprised on two fronts: filling takes days, not hours, and the water isn't free. A single garden hose at ~9 GPM moves about 540 gallons an hour, so a typical in-ground pool is a 30-50 hour fill — plan for the hose to run overnight, and consider two hoses on separate spigots to halve the time. The water bill is the smaller shock: at typical municipal rates of $4-$10 per 1,000 gallons, a 20,000-gallon fill runs $80-$200. Two money-saving calls before you start: ask your utility about a pool-fill adjustment (many waive the sewer charge, which is often half the bill, for water that never enters the drain), and check for drought or fill restrictions — some districts limit or ban pool filling in summer, and a bulk-water delivery truck may be the legal (and sometimes faster) alternative.

Frequently asked questions

How many gallons is a 16 x 32 pool?

With a 3 ft shallow end and an 8 ft deep end (5.5 ft average depth), a 16 × 32 ft rectangular pool holds about 21,000 gallons: 16 × 32 × 5.5 = 2,816 cubic feet, times 7.48 gallons per cubic foot. A shallower 3-to-5-ft version of the same pool holds closer to 15,300 gallons.

How long does it take to fill a pool with a garden hose?

A typical garden hose delivers around 9 gallons per minute, or about 540 gallons an hour. A 21,000-gallon pool therefore takes roughly 39 hours — a day and a half of continuous running. Running two hoses roughly halves it.

How much does it cost to fill a swimming pool?

Municipal water commonly runs $4-$10 per 1,000 gallons, so a 20,000-gallon pool costs about $80-$200 to fill from the tap. Check your utility bill for the exact rate, and ask about a pool-fill adjustment — some utilities waive the sewer portion for water that never goes down the drain.

How do I calculate the average depth of a pool?

Add the shallow end depth to the deep end depth and divide by 2 — a 3 ft shallow end and 8 ft deep end average 5.5 ft. This works because a steadily sloping floor holds the same water as a flat floor at the midpoint depth. If your pool is one depth everywhere, just use that depth.

Why does an oval pool use a 0.89 factor instead of the ellipse formula?

Most 'oval' pools aren't true ellipses — they're closer to a rectangle with rounded ends, so they hold more water than the mathematical ellipse factor (0.785) predicts. The pool industry's standard 0.89 multiplier on length × width splits the difference and matches real pools well.

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