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Round Pool Volume Calculator

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Our round pool volume calculator helps you estimate the volume of your swimming pool. It also works as an oval pool volume calculator, allowing you to change the pool shape from circular to elliptical.

Whether you’ve just bought a round above-ground pool or have an oval in-ground pool in your backyard, our tool will calculate the amount of water needed to fill it, in gallons or liters. If you want to estimate the filling cost, this calculator will tell you how much you can expect to spend on water to fill up your backyard oasis 💦

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Check out our other useful swimming pool tools before diving in!

How to calculate round pool volume

To learn how to calculate pool volume, the first step is to identify the exact 3D shape we’re dealing with.

There are two key factors to consider here:

  • Does the pool have a round or an oval cross-section?
  • Is the depth constant, or does it vary?

Let’s go through all these combinations, one by one:

1. Round pool, constant depth

The easiest scenario is a round above-ground pool, as it has one, constant depth. In this case, it’s simply a large cylinder filled with water, so we need the cylinder volume formula to calculate the volume of water.

V=π×(l2)2×dV = \pi\times \left(\frac{l}{2}\right)^2 \times d

where:

  • VV — Pool volume;
  • ll — Length of the pool (diameter); and
  • dd — Water depth.

2. Round pool, varied depth

It gets a bit trickier if your circular pool doesn’t have the same depth, which may be the case for some in-ground pools. In such a situation, we need to know the depth of the shallow and deep ends of the swimming pool — and then calculate the average of these two values:

V=π×(l2)2×d1+d22V = \pi\times \left(\frac{l}{2}\right)^2 \times \frac{d_1 + d_2}{2}

where:

  • d1d_1 — Depth at one end of the pool; and
  • d2d_2 — Depth at another end of the pool.

🙋 Typical values for backyard pools are 3-4 ft for the shallow end, and 5-6 ft for the deep end.

Find the volume of an oval pool

In the above section, we covered round pools. Let’s move to oval pools!

3. Oval pool, constant depth

The typical design of an oval above-ground pool has a flat bottom, meaning the depth is constant at every point. The formula for oval pool volume will look as follows:

V=π×l×w4×dV = \frac{\pi\times l\times w}{4} \times d

where:

  • ww — Width of the pool (the other axis of an oval);

The first part comes from the ellipsis area formula:

A=π×a×b\small A = \pi \times a\times b

where a\small a, b\small b are distances from the center of the ellipse to its vertices along the horizontal and vertical axes.

Since the calculator uses the full length and width of the oval (l=2a\small l = 2a, w=2b\small w =2b), the ellipse area formula must be adjusted by dividing the product by 4.

4. Oval pool, varied depth

This is the general formula — you can use it for all the previously discussed pool shapes:

V=π×l×w4×d1+d22V = \frac{\pi\times l\times w}{4} \times \frac{d_1 + d_2}{2}

You are getting simpler equations when some variables are equal (e.g., l=w\small l = w for round pools, and d=d₁=d₂\small d = d₁ = d₂ for flat-bottom pools).

🔎 If your pool is in a different shape than round 🔵 or oval ⬭, please check our pool calculator for standard rectangular pools, or versatile tank volume calculator that covers plenty of other shapes.

FAQs

How many gallons are in a 24 foot round pool?

It depends on how deep your 24 ft round pool is and if you fill it halfway, to the brim, or leave a few inches below the top. Most above-ground round pools have wall heights of 48 to 54 inches (4 to 4.5 ft) — but remember to leave 4 to 6 inches to prevent splashing and overflowing.

Approximate water capacities for several common water depths:

  • 3 ft: ~10,150 gallons
  • 3.5 ft: ~11,840 gallons
  • 4 ft: ~13,540 gallons
  • 4.5 ft: ~15,230 gallons
  • 5 ft: ~16,920 gallons

For other water depths — or pools with depth profiles — you can estimate the water volume in no time using our round pool volume calculator.

How many gallons are in a 18 foot round pool?

There’s no single answer — it depends on water depth. Assuming a standard above-ground pool with a flat bottom:

  • 3 ft: ~5,710 gallons
  • 3.5 ft: ~6,660 gallons
  • 4 ft: ~7,600 gallons
  • 4.5 ft: ~8,570 gallons
  • 5 ft: ~9520 gallons

How do I measure a round pool?

Take a measuring tape and follow these simple steps:

  1. Measure the diameter (pool length) — measure straight across the pool from one side to the other, passing through the center.
  2. Measure the depth:
    • Measure water depth from the pool bottom to the water surface. Alternatively, measure the total depth (wall height for round above-ground pools) and subtract 4-6 inches to estimate the optimal water depth.
    • For variable depth pools, measure shallow and deep ends separately.
  3. Calculate the volume — either by hand or with an online round pool volume calculator — to find out the water needed.