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.