Swimming Pool Volume Calculator

Swimming pool volume is the foundation for every chemical dosage calculation. Chlorine, pH adjusters, alkalinity, calcium hardness, and shock treatments are all dosed per 10,000 gallons. Get the volume wrong and every dose you measure afterward is wrong by the same margin.

Volume formulas by pool shape:

Rectangular pool: V = Length × Width × Average Depth × 7.48 (7.48 converts cubic feet to gallons)

Average Depth ≈ (Shallow End Depth + Deep End Depth) ÷ 2, but only for a floor that slopes evenly end to end. See the note below on why real pools come in under that.

Oval pool: V = Length × Width × Average Depth × 5.9 (π ÷ 4 × 7.48 ≈ 5.9)

Round pool: V = π × (Diameter ÷ 2)² × Depth × 7.48 Or simplified: V = Diameter² × 5.9 × Depth

Kidney/freeform pool: Divide into geometric sections, calculate each, sum totals.

What each variable means:

• 7.48: gallons per cubic foot (1 cubic foot = 7.480519 gallons)
• Average depth: the input people get wrong most often. If the floor slopes evenly from end to end, the simple midpoint is exact. Real pools are not built that way. They have a long flat shallow shelf and a short deep hopper, so most of the floor sits at the shallow depth and the true average lands below the midpoint. Wade out and measure the depth at three or four points along the length, then average those.
• Actual vs. geometric volume: walls are usually vertical through the shallow end before the floor breaks into the slope, so a single measurement at each end will not describe the pool.

Reference: chemical dosing per 10,000 gallons:

• Calcium hypochlorite, 1 lb of 65% cal-hypo: raises free chlorine by about 7.5 ppm. Strength matters here. The same pound of 73% product gives roughly 8.8 ppm, so read the label before you scoop.
• Muriatic acid (1 quart): lowers pH by ~0.2 units in 10,000 gal (varies with alkalinity)
• Baking soda (1.5 lbs): raises total alkalinity by ~10 ppm
• Calcium chloride, 1.2 lbs of the 77% flake sold at most pool shops: raises calcium hardness by about 10 ppm. Anhydrous 94–100% product does the same job at roughly 15 oz.

Worked example: Rectangular pool: 32 ft × 16 ft. Shallow end: 3.5 ft, deep end: 8.5 ft, measured average depth 6.0 ft.

• Volume = 32 × 16 × 6.0 = 3,072 cubic feet
• 3,072 × 7.48 = 22,978 gallons, about 23,000. The calculator carries 7.480519 and returns 22,980, so expect a couple of gallons of difference against hand arithmetic.

To raise free chlorine by 3 ppm with 65% calcium hypochlorite:

• Pounds needed = (23,000 ÷ 10,000) × 3 ÷ 7.5 = 2.3 × 0.4 = 0.92 lbs
• Call it a pound, and add it in the evening with the pump running. Sunlight burns off free chlorine fast, so a midday dose is half wasted.