How Much Chlorine

Pool Volume Calculator (Gallons for Rectangle, Round and Oval Pools)

By Tam Vu · Updated

On this page
  1. The formulas
  2. Worked examples
  3. Quick reference
  4. Why it matters

Every pool chemical dose depends on how much water you are treating. Get the gallons right first, and the chemical calculator can do the rest.

Pool volume

Measure the water, not the pool wall: use the depth from the water line to the floor. For a pool with one depth, enter it in both depth boxes.

The formulas

Three pool shapes with their volume formulas: rectangle uses length times width, round uses 3.1416 times radius squared, oval uses 3.1416 times half the length times half the width; each is multiplied by average depth and 7.48 gallons per cubic foot.
Surface area × average depth × 7.48 gallons per cubic foot.

A cubic foot holds 7.48 US gallons (7.48052 to more decimal places; the calculator and the examples on this page use 7.48052, and the formulas show it rounded to 7.48). So the volume is the surface area in square feet, times the average depth in feet, times 7.48.

Shape Surface area Gallons
Rectangle length × width length × width × average depth × 7.48
Round 3.1416 × (diameter ÷ 2)² 3.1416 × radius² × average depth × 7.48
Oval 3.1416 × (length ÷ 2) × (width ÷ 2) 3.1416 × half-length × half-width × average depth × 7.48

Average depth = (shallow end + deep end) ÷ 2. This assumes the floor slopes evenly from one end to the other. A pool with a long flat shallow area and a short deep hopper holds less than this estimate, so treat the result as approximate.

Worked examples

  • Rectangle, 32 × 16 ft, 3.5 to 8 ft deep. Average depth = (3.5 + 8) ÷ 2 = 5.75 ft. 32 × 16 × 5.75 × 7.48 = 22,023 gallons.
  • Round above-ground pool, 24 ft across, 4 ft of water. Radius 12 ft. 3.1416 × 12 × 12 × 4 × 7.48 = 13,536 gallons.
  • Oval, 30 × 15 ft, 4 to 5 ft deep. Average depth 4.5 ft. 3.1416 × 15 × 7.5 × 4.5 × 7.48 = 11,897 gallons.

Quick reference

Pool Gallons
Round, 15 ft, 4 ft of water 5,288
Round, 18 ft, 4 ft of water 7,614
Round, 24 ft, 4 ft of water 13,536
Rectangle, 20 × 10 ft, 4 ft deep 5,984
Oval, 30 × 15 ft, 4 to 5 ft deep 11,897

These are computed with the formulas above. Your pool's real water level may be lower than the wall height, so measure your own.

Why it matters

Doses scale directly with volume. If you think your pool holds 15,000 gallons but it really holds 22,000, every dose you add will be about a third too small. Once you have the number, use it in the pool chemical calculator.