Pool Gallon Calculator
Discover exactly how much water your swimming pool holds. Ideal for accurately dosing chemicals, buying pool salt, or sizing your next pool heater. We support rectangular, round, and oval shapes perfectly.
Last updated: February 26, 2026
*If your pool has a flat bottom, enter the same depth for both shallow and deep ends.
When To Use The Pool Gallon Calculator
Ideal for
Standard Maintenance
Adding too much chemical can cause skin irritation, while adding too little leaves algae. Correct volume is key.
Ideal for
Saltwater Gens
Changing from chlorine to salt? You'll need the exact gallon count to avoid over-salinating the water.
Ideal for
Upgrades & Fixes
A heater rated for a 15,000-gallon pool won't work correctly on a 25,000-gallon pool.
How Pool Volume is Computed
Unlike a simple box, most swimming pools have sloped floors that go from shallow to deep. Because of this, calculating the water volume requires finding an Average Depth before multiplying by the overall surface area.
The Core Math Formulations
Average Depth = (Shallow Depth + Deep Depth) ÷ 2Rectangular = Length × Width × Average Depth × 7.5Round = Diameter × Diameter × Average Depth × 5.9Oval = Long Diameter × Short Diameter × Average Depth × 5.9The multiplier "7.5" represents the number of gallons in one cubic foot. For circular and oval shapes, the multiplier changes to "5.9", which factors in both Pi (3.14) and the gallons-per-cubic-foot logic.
Tips for Accuracy
- Measure at the water line: Don't measure to the top of the pool wall. Measure from where the water actually rests.
- Free-form pools: Calculate the average width, multiple by the length, by the average depth, and use the 7.5 multiplier. Try mapping it out into smaller squares if necessary.
- Flat bottoms: Simply use your flat depth for both the shallow and deep inputs!
Common Size Example
A classic 16x32 Rectangular Pool averaging 5.5 ft deep:
Total Volume
21,120 Gallons
Frequently Asked Questions
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