Pool Ratio

21 ft round pool: how many gallons?

A 21 ft round pool with 4 ft of water holds about 10,360 US gallons (39,231 litres). Here is what that means for salt and chemicals.

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

Volume
10,360 gal
39,231 litres · 4 ft of water
Salt to 3,200 ppm (new salt pool)277 lb · 7 × 40 lb bags
10% liquid chlorine per +1 ppm13 fl oz
Stabilizer 0 → 40 ppm3.5 lb
Baking soda per +10 ppm alkalinity1.5 lb
Calcium chloride (77%) per +10 ppm20 oz

Open the chemical calculator for this pool →

The maths

  1. Area = π × 10.5² = 346.4 sq ft
  2. Volume = 346.4 × 4 = 1,385 cu ft
  3. 1,385 cu ft × 7.48 gal per cu ft

= 10,360 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 21 ft round pool?

About 10,360 US gallons (39,231 litres) with 4 ft of water.

How much salt does a 21 ft round pool need?

About 277 lb (126 kg) to bring fresh water to 3,200 ppm, or 7 bags of 40 lb. Check your salt cell’s target first.

How much chlorine does a 21 ft round pool need?

Each +1 ppm of free chlorine takes about 13 fl oz of 10% liquid chlorine. With stabilizer at 40 ppm, keep free chlorine around 4.6 ppm.

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