How to Calculate Pool Volume in Gallons (All Pool Shapes)
Why Accurate Pool Volume Matters
Knowing your exact pool volume is essential for proper chemical dosing. Too little chlorine leaves your pool vulnerable to algae and bacteria. Too much can irritate skin and eyes and damage pool equipment.
Pump and filter sizing depends on pool volume. Your filtration system should turn over the entire pool volume at least once every 8-12 hours. An undersized pump leaves water stagnant; an oversized pump wastes energy.
Heater sizing requires volume calculations. A pool heater needs to warm every gallon of water, so incorrect volume estimates lead to systems that are too slow to heat or too expensive to operate.
Rectangular Pool Formula
Length × Width × Average Depth × 7.48 = Volume in gallons. The multiplier 7.48 converts cubic feet to gallons.
For pools with a consistent slope from shallow to deep end, the average depth is simply (shallow depth + deep depth) ÷ 2. A pool that is 3 feet at the shallow end and 8 feet at the deep end has an average depth of 5.5 feet.
Example: a 30×15 foot pool with an average depth of 5.5 feet = 30 × 15 × 5.5 × 7.48 = 18,513 gallons.
Round and Oval Pool Formulas
Round pools: Diameter × Diameter × Average Depth × 5.9 = Volume in gallons. The constant 5.9 combines the circular area formula (π/4) with the gallons conversion.
Oval pools: Long Diameter × Short Diameter × Average Depth × 5.9 = Volume in gallons. This uses the same constant as round pools since an oval is simply a stretched circle.
Example: a 24-foot round above-ground pool at 4 feet deep = 24 × 24 × 4 × 5.9 = 13,594 gallons.
Chemical Dosing by Pool Size
Chlorine: 1 ppm (part per million) of free chlorine requires about 0.00013 ounces of pure chlorine per gallon. For a 15,000-gallon pool, raising chlorine by 1 ppm needs about 2 ounces of liquid chlorine (sodium hypochlorite at 12.5%).
pH adjustment: to lower pH by 0.2 in a 15,000-gallon pool, you need approximately 1-1.5 cups of muriatic acid. To raise pH by 0.2, use about 6-8 ounces of soda ash.
Shock treatment: standard pool shock uses 1 pound of calcium hypochlorite per 10,000 gallons. Double the dose for visible algae. Always shock at dusk to prevent UV degradation of the chlorine.
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