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how many gallons is my pool

You can estimate how many gallons are in your pool with a simple formula once you know its length, width, and average depth in feet.

How Many Gallons Is My Pool?

Step 1: Measure Your Pool

Grab a tape measure and note:

  • Length (in feet)
  • Width (in feet)
  • Shallow-end depth (in feet)
  • Deep-end depth (in feet)

If the bottom slopes, find average depth :

  • Average depth = (shallow depth+deep depth)/2(\text{shallow depth}+\text{deep depth})/2(shallow depth+deep depth)/2

Example: Shallow 3 ft, deep 7 ft → (3+7)/2=5(3+7)/2=5(3+7)/2=5 ft average depth.

Step 2: Use the Right Formula

All formulas are just:
Length × Width × Average Depth × a shape multiplier = gallons (US).

1. Rectangular or Square Pools

Use this if your pool is roughly a rectangle.

  • Formula:
    Gallons = Length × Width × Average Depth × 7.5

Example:

  • 16 ft × 32 ft, 3 ft shallow, 7 ft deep
  • Average depth = (3+7)/2=5(3+7)/2=5(3+7)/2=5 ft
  • Gallons = 16 × 32 × 5 × 7.5 = 19,200 gallons (approx).

2. Round Pools

Use this if you have a circular above-ground or in-ground pool.

  • First find radius = diameter ÷ 2.
  • Formula:
    Gallons = 3.14 × Radius × Radius × Average Depth × 7.5

Example:

  • 18 ft round, single depth 4 ft
  • Radius = 18 ÷ 2 = 9 ft
  • Gallons = 3.14 × 9 × 9 × 4 × 7.5 ≈ 7,630 gallons.

3. Oval Pools

For oval above-ground or in-ground pools:

  • Formula (common version):
    Gallons = Length × Width × Average Depth × 6.7
  • Another version uses π/4:
    Gallons ≈ 3.14 × Length × Width × 0.25 × Average Depth × 7.5.

Example:

  • 12 ft × 24 ft oval, depth about 4.3 ft
  • Gallons ≈ 12 × 24 × 4.3 × 6.7 ≈ 8,300 gallons.

4. Kidney or Free‑Form Pools

If your pool has “curvy” sides:

  • Measure the two widest points (A and B).
  • Kidney shape formula:
    Gallons = (A + B) × Length × 0.45 × Average Depth × 7.5
  • For very irregular/free‑form pools, one common shortcut is:
    Gallons ≈ Longest Length × Widest Width × Average Depth × 5.9.

These give an approximation, but it’s usually close enough for chemicals and equipment sizing.

Helpful Reference Numbers

Many standard pools fall in these rough ranges:

  • 12 × 24 ft rectangle, 4 ft avg depth → around 8,600 gallons.
  • 16 × 32 ft rectangle, 4 ft avg depth → around 15,400 gallons.
  • 18 × 36 ft rectangle, 4 ft avg depth → around 19,400 gallons.
  • 24 ft round, ~4 ft water depth → about 12,000–13,500 gallons.

These are just examples to sanity‑check your own calculation.

Mini “Forum-Style” Tip

If you’re dosing chemicals and not sure your volume is perfect, many pool owners slightly underestimate gallons at first, test the water after dosing, then adjust. This helps avoid over-chlorinating while you dial in your true volume.

Quick Story-Style Example

Imagine you’ve just moved into a house with a classic backyard rectangle pool. You measure it: 20 ft long, 40 ft wide, 3.5 ft shallow, 7.5 ft deep.

  • Average depth = (3.5+7.5)/2=5.5(3.5+7.5)/2=5.5(3.5+7.5)/2=5.5 ft.
  • Gallons = 20 × 40 × 5.5 × 7.5 = 33,000 gallons (approx).

Now you know what size pump and heater to look at, and how much chlorine or shock to add without guessing.

Simple HTML Table: Example Volumes

Here’s a quick HTML table with some standard in‑ground rectangle examples.

html

<table>
  <thead>
    <tr>
      <th>Pool Size (ft)</th>
      <th>Average Depth (ft)</th>
      <th>Approx. Gallons</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>12 x 24</td>
      <td>4.0</td>
      <td>≈ 8,600</td>
    </tr>
    <tr>
      <td>16 x 32</td>
      <td>4.0</td>
      <td>≈ 15,400</td>
    </tr>
    <tr>
      <td>18 x 36</td>
      <td>4.0</td>
      <td>≈ 19,400</td>
    </tr>
    <tr>
      <td>20 x 40</td>
      <td>5.0</td>
      <td>≈ 30,000</td>
    </tr>
  </tbody>
</table>

Values are rounded examples based on common charts.

Quick TL;DR

  • Measure length, width, shallow and deep depths in feet.
  • Find average depth if the pool slopes.
  • Use the rectangle formula for most regular pools:
    Gallons = Length × Width × Average Depth × 7.5.
  • For round, oval, or irregular pools, use the matching shape formulas above for a solid estimate.

If you send me your pool’s shape + length + width + shallow & deep depths, I can calculate a more precise gallon estimate for you.
Information gathered from public forums or data available on the internet and portrayed here.