Pool Ratio

18 × 40 ft oval pool: how many gallons?

A 18 × 40 ft oval pool with 4 ft of water holds about 16,920 US gallons (64,051 litres). Here is what that means for salt and chemicals.

Last updated · Checked against published product doses · How we calculate

Volume
16,920 gal
64,051 litres · 4 ft of water
Salt to 3,200 ppm (new salt pool)452 lb · 12 × 40 lb bags
10% liquid chlorine per +1 ppm22 fl oz
Stabilizer 0 → 40 ppm5.6 lb
Baking soda per +10 ppm alkalinity2.4 lb
Calcium chloride (77%) per +10 ppm33 oz

Open the chemical calculator for this pool →

The maths

  1. Area = π × 20 × 9 = 565.5 sq ft
  2. Volume = 565.5 × 4 = 2,262 cu ft
  3. 2,262 cu ft × 7.48 gal per cu ft

= 16,920 US gallons

Real pools vary: water levels sit a few inches below the wall top, floors slope and corners are rounded. If your pool’s depth differs, adjust it in the volume calculator.

Frequently asked questions

How many gallons is a 18 × 40 ft oval pool?

About 16,920 US gallons (64,051 litres) with 4 ft of water.

How much salt does a 18 × 40 ft oval pool need?

About 452 lb (205 kg) to bring fresh water to 3,200 ppm, or 12 bags of 40 lb. Check your salt cell’s target first.

How much chlorine does a 18 × 40 ft oval pool need?

Each +1 ppm of free chlorine takes about 22 fl oz of 10% liquid chlorine. With stabilizer at 40 ppm, keep free chlorine around 4.6 ppm.

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