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Pool Volume Calculator
Calculate your pool size in gallons — required for all chemical calculations.
Works for rectangular, oval, round, and kidney-shaped pools.
No sign-ups. Instant results.
💡 Tip: Write down your pool volume — you'll need it for every other calculator.
Example calculation
Let's calculate the volume of a typical rectangular pool:
| Measurement | Value |
|---|---|
| Length | 30 feet |
| Width | 15 feet |
| Shallow end depth | 3 feet |
| Deep end depth | 8 feet |
| Average depth | 5.5 feet (3 + 8) ÷ 2 |
| Pool volume | 18,562 gallons |
Formula: 30 × 15 × 5.5 × 7.5 = 18,562 gallons
Pool volume formulas by shape
Rectangular pools
Formula: Length × Width × Average Depth × 7.5 = Gallons
Why 7.5? There are 7.5 gallons in one cubic foot of water.
Round pools
Formula: Diameter × Diameter × Average Depth × 5.9 = Gallons
Why 5.9? This accounts for the circular area (π × radius²) and converts to gallons.
Oval pools
Formula: Length × Width × Average Depth × 5.9 = Gallons
Similar to round pools but uses length and width instead of diameter.
Kidney or irregular shaped pools
For irregular shapes, measure the longest length and widest width, then multiply by 0.85 to account for the curved sections. Or divide the pool into sections (rectangular + round) and add them together.
How to measure your pool accurately
📏 Use a measuring tape
A 50-100 foot measuring tape works best. Walk the perimeter and measure straight lines for length and width.
💧 Measure water depth
Always measure to the actual water level, not the pool height. Use a pole or weighted string to measure depth.
📐 Calculate average depth
For sloped pools: (shallow depth + deep depth) ÷ 2. Example: (3ft + 8ft) ÷ 2 = 5.5ft average.
🔄 Measure multiple times
Measure twice to ensure accuracy. Being off by a foot can mean 1,000+ gallons difference in calculations.
💡 Use a reliable pool test kit to verify your pool volume calculation is accurate by testing how chemicals affect your water.
Pool volume calculator FAQs
How do I calculate my pool volume in gallons?
Measure your pool's length, width, and depth. For rectangular pools, multiply length × width × average depth × 7.5. For round pools, multiply diameter × diameter × average depth × 5.9. Our calculator does the math automatically.
Why do I need to know my pool volume?
Pool volume determines how much of each chemical to add. Adding the wrong amount can make your pool unsafe to swim in or damage your equipment. Accurate volume measurements ensure proper chemical balance.
What if my pool has a sloped bottom?
Measure the shallow end depth and deep end depth. Add them together and divide by 2 to get average depth. For example, if the shallow end is 3 feet and deep end is 8 feet, the average depth is 5.5 feet.
Do I measure to the top of the pool or the water line?
Always measure to the actual water depth, not the height of the pool walls. Measure from the water surface down to the bottom at both the shallow and deep ends.
Can I use this calculator for hot tubs?
Yes, but for hot tubs and spas, we recommend using our dedicated Hot Tub Calculator which accounts for spa-specific chemistry needs.
How accurate does my pool volume need to be?
Try to be within 500 gallons for pools under 20,000 gallons, and within 1,000 gallons for larger pools. Small errors in measurement (1-2 feet) can result in significant volume differences.
What if my pool is an irregular shape?
For kidney-shaped or freeform pools, select "Kidney / Irregular" in the calculator. Measure the longest length and widest width. The calculator will estimate volume using these dimensions. For very complex shapes, you may need to divide the pool into sections and calculate each separately.