Pool Volume Calculator - Gallons, Litres & Chlorine Dose

How to use this tool

1. Select a rectangular, oval, round, or kidney pool shape.
2. Enter the dimensions and either average depth or shallow and deep endpoint depths.
3. Read the estimated volume, flow targets, and rough initial shock amount.

Pool volume formulas

These formulas estimate gallons from measured water dimensions. Enter lengths in feet for the equations below; the calculator converts metric measurements to feet before calculating. For a sloped floor, the single average depth is the midpoint of the shallow and deep measurements.

• Rectangular: Length × Width × Average Depth × 7.48052 gallons/cu ft
• Circular: π × Radius² × Average Depth × 7.48052
• Oval: (π ÷ 4) × Length × Width × Average Depth × 7.48052
• Kidney: 0.45 × Length × (Width A + Width B) × Average Depth × 7.48052

The kidney factor is a plan-view approximation based on two width measurements. Free-form pools can depart substantially from this outline, so divide an irregular footprint into rectangular sections when that better matches its shape. For chemical treatment, use the pool builder’s volume or a measured fill estimate when available.

Chemical dosing context

Accurate pool volume is essential for correct chemical dosing. Overdosing chlorine can cause skin/eye irritation; underdosing allows bacterial and algae growth. A 10% volume error means a 10% error in every chemical calculation. Typical pools:

• Small residential (12×24 ft): ~8,600 gallons
• Medium residential (16×32 ft): ~18,700 gallons
• Olympic (50m): ~660,000 gallons

How to measure irregular pools

For free-form or L-shaped pools, break the footprint into rectangles and sum their volumes. For an L-shape, measure each rectangular section separately. The kidney option uses a common approximation, but a single pair of widths cannot describe every contour. A more detailed section-by-section estimate or builder-provided volume is preferable when the number will guide chemical treatment. Do not compensate for uncertain geometry by automatically adding chemicals; test the water and follow the product directions.

Chemical dosing reference

These reference amounts vary by product and water conditions. Always test the water and follow the product label; volume estimates alone do not determine the correct treatment.

Turnover rate

The recommended practice is for all pool water to circulate through the filter at least once every 6–8 hours (daily turnover). To find the required pump flow rate in gallons per minute (GPM):

GPM = Pool Volume (gallons) ÷ Turnover Time (minutes)

The live result also shows flow targets for 8-hour and 6-hour turnover. For example, a 20,000-gallon pool needs about 41.7 GPM to move that volume in 8 hours (20,000 ÷ 480). These are planning figures; a pump's installed flow changes with plumbing, filter condition, fittings, and system head. Check the equipment specifications and consult a pool professional when sizing a system.