Pool Volume Calculator
Free pool volume calculator: calculate gallons in rectangular, round, oval, kidney, and L-shaped pools. Essential for chemical dosing, salt system set
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Pool Volume Formulas by Shape
The pool volume calculator converts pool dimensions to gallons (1 cubic foot = 7.48 gallons). "Pool volume calculator" gets 18K monthly searches. Basic rectangular formula: Volume (gal) = Length (ft) × Width (ft) × Average Depth (ft) × 7.48.
- Rectangular pool: L × W × Avg Depth × 7.48. Example: 20'×40'×5' avg = 29,920 gal
- Round pool: Diameter2 × 0.7854 × Depth × 7.48. 24-ft diameter, 4-ft deep = 13,593 gal
- Oval pool: L × W × 0.7854 × Avg Depth × 7.48. 18'×33', 4' avg = 13,959 gal
- Kidney-shaped: (Width1 + Width2)/2 × Length × 0.45 × Avg Depth × 7.48
- L-shaped: Calculate each rectangular section separately and add together
Common Pool Sizes and Their Volumes
- 12×24 ft (3.5' avg depth): 7,489 gallons — small in-ground pool
- 16×32 ft (5' avg depth): 19,149 gallons — popular mid-size
- 20×40 ft (5.5' avg depth): 32,912 gallons — large residential
- 15-ft round above-ground (4' deep): 5,310 gallons
- 18-ft round above-ground (4' deep): 7,646 gallons
- 24-ft round above-ground (4' deep): 13,593 gallons
- 27-ft round above-ground (4' deep): 17,205 gallons
- Lap pool (8×40 ft, 4' avg): 9,574 gallons
Why Accurate Pool Volume Matters
Every chemical dosage is calculated per gallon — errors cascade. Using an overstated volume under-doses; understated over-doses. Key dosages per 10,000 gallons:
- Liquid chlorine (12.5%): 1 quart raises free chlorine ~1–2 ppm
- Shock (calcium hypochlorite 68%): 1 lb raises chlorine ~6–7 ppm
- Muriatic acid (31.45%): 1 quart lowers pH ~0.4 units
- Baking soda: 1.5 lbs raises alkalinity ~10 ppm
- Calcium chloride: 2 lbs raises calcium hardness ~20 ppm
Calculating Average Depth for Variable-Depth Pools
Most in-ground pools have a shallow end, transition slope, and deep end. For accurate volume:
- Simple slope: Average depth = (shallow + deep) / 2. 3.5' shallow, 9' deep → avg = 6.25'
- Flat shallow + slope + flat deep: Calculate each section separately (volume = section L × W × section avg depth × 7.48), then add all sections
- Builder's spec: Check pool equipment area or skimmer housing — many builders post a spec sheet with total volume
Frequently Asked Questions About Pool Volume
Does the spa/hot tub count in total pool volume?
Yes, if the spa shares water with the pool (spillover spa connected to the pool circulation system). A typical attached spa adds 250–600 gallons. For a 15,000-gallon pool with a 400-gallon spa, use 15,400 gallons total for all chemical calculations and when setting up your salt chlorine generator's target output.
How do I measure my above-ground pool's depth accurately?
Most above-ground pools are filled to 6–12 inches below the top wall — not the full wall height. Measure actual water depth at the center of the pool, not the wall height. A 54-inch wall pool is often filled to 48 inches (4 ft) of actual water. Use the actual water depth in all volume calculations — using the wall height overstates volume by up to 15%.