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How to Calculate Pool Volume

Pool volume = the gallons of water your pool holds. Every chemical dose on this site scales with your gallons, so getting volume right is the foundation of accurate pool chemistry. Use the calculator below for an instant answer, then read on for the formula behind your shape.

Select your pool shape

Rectangular (uniform depth)

Average depth = (shallow end + deep end) ÷ 2

Supported Pool Shapes & Formulas

  • RectangularLength × Width × Average Depth × 7.48
  • Roundπ × Radius² × Depth × 7.48
  • Ovalπ × (Length / 2) × (Width / 2) × Depth × 7.48
  • Kidney(Width A + Width B) × Length × Avg Depth × 0.45 × 7.48Two-width approximation; estimate only.
  • L-ShapeSum of two rectangles, then × 7.48
  • Freeform / OtherEstimate using closest regular shape, or fill / meter test

All calculations use 7.48 gallons per cubic foot (per NIST definition: 7.48052 US gallons in that volume). Some older sources round to 7.5, which introduces a 0.3% error that compounds across a pool. We round to 7.48 for cleaner math.

How to Measure Your Pool

  1. Length and width: measure at the water line, not the coping or deck edge. A long tape measure stretched along the longest and widest points is more accurate than estimating from satellite imagery.
  2. Depth: if your pool has a shallow end and a deep end, average them: (shallow + deep) ÷ 2. For a 3 ft shallow + 8 ft deep pool, average depth is 5.5 ft.
  3. Above-ground pools: measure actual waterdepth, not wall height. Most above-ground pools are filled 6–12 inches below the top of the wall (per typical manufacturer installation guidance from Intex, Bestway, and similar above-ground brands, which specify filling to roughly the bottom of the top rail or skimmer opening).
  4. Round pools: measure the diameter (across the widest point). Radius is half the diameter, and the calculator handles that conversion automatically.
  5. Freeform / kidney pools: these formulas are approximations. If you want a precise number, the most accurate method is a water-meter fill test: note the meter reading, fill the pool, note the new reading, subtract.

Why Pool Volume Matters

Every chemical dose scales with volume. A 10% volume error means a 10% dose error, every week, forever. Under-dose: algae creeps in. Over-dose: irritated swimmers, damaged liners, or saturation indices that pit plaster and corrode metal. Measure once. Years of accurate dosing follow.

Once you have a number, the volume above is saved to your Pool Card. Every other calculator on this site (chlorine, salt, pH, shock, CYA, calcium hardness, alkalinity) automatically pre-fills with it, so you only enter your gallons once.