Home Pool Volume Calculator
Pool Volume Calculator — How Many Gallons Is My Pool?
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.
💡 Quick answer — pool volume formulas
Rectangular pool: Length × Width × Avg Depth × 7.4805 = gallons
Round pool: Diameter² × Avg Depth × 5.8752 = gallons
Oval pool: Length × Width × Avg Depth × 5.8752 = gallons
Average depth: (Shallow depth + Deep depth) ÷ 2
18 ft round pool (4 ft deep) → ~7,614 gal | 21 ft round pool (4 ft deep) → ~10,364 gal
18×33 oval pool (4 ft deep) → ~13,959 gal | 18×54 oval pool (4 ft deep) → ~22,842 gal
Measurements and irregular shapes introduce uncertainty, so use the result as a practical dosing estimate.
💡 Tip: Write down your pool volume — you'll need it for every other calculator.
Know your volume — now get your chemicals ready:
- Pool test kit — measure chlorine, pH, and alkalinity before dosing
- Liquid chlorine — most common first chemical needed after calculating volume
- Pool chemical starter kit — everything needed for opening season
Example calculation
For a 30 × 15 ft rectangular pool that slopes from 3 ft to 8 ft deep:
| 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 |
| Estimated pool volume | ~18,514 gallons |
Formula: 30 × 15 × 5.5 × 7.4805 ≈ 18,514 gallons. Actual usable water volume can differ because of steps, benches, slopes, coves, and measurement error.
Pool volume formulas by shape
Rectangular pools
Formula: Length × Width × Average Depth × 7.4805 = gallons.
The conversion factor is about 7.4805 US gallons per cubic foot.
Round pools — how many gallons by diameter
Formula: Diameter² × Average Depth × 5.8752 = gallons.
This combines circular area (π × radius²) with the cubic-foot-to-gallon conversion.
Examples: 18 ft round (4 ft deep) ≈ 7,614 gal | 21 ft ≈ 10,364 gal | 24 ft ≈ 13,536 gal.
Oval pools — gallons for common sizes
Formula: Length × Width × Average Depth × 5.8752 = gallons for a true elliptical footprint.
Examples: 18×33 oval (4 ft deep) ≈ 13,959 gal | 18×54 oval (4 ft deep) ≈ 22,842 gal.
Kidney or irregular shaped pools
The calculator applies a rough 0.85 shape factor to the longest length, widest width, and average depth. Treat that result as an estimate, not a geometric exact value. For a complex freeform pool, divide the footprint into simpler sections and add the section volumes, or use build plans/water-meter data when available.
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 the water's length, width or diameter, and average depth. A rectangular pool is length × width × average depth × 7.4805. A round pool is diameter² × average depth × 5.8752. The calculator applies these geometry conversions automatically.
Why do I need to know my pool volume?
Most chemical and equipment calculations scale with water volume. A better volume estimate reduces dosing error and gives the chlorine, pH, salt, filter-size, and other calculators a more reliable starting point.
What if my pool has a sloped bottom?
For a simple, even slope, average the shallow and deep water depths: (shallow + deep) ÷ 2. Complex hopper bottoms, benches, and multiple slopes can make that approximation less accurate.
Do I measure to the top of the pool or the water line?
Measure the actual water depth, not the wall height. Chemical dosing depends on the amount of water currently in the pool.
Can I use this calculator for hot tubs?
You can estimate a simple rectangular or round vessel, but for chemical dosing use the dedicated Hot Tub Calculator, which is designed for spa-size volumes and spa chemistry.
How accurate does my pool volume need to be?
More accurate is better, but every field measurement is an estimate. Measure carefully, use actual water depth, and treat freeform-pool results as approximate. If a chemical label says to add in stages and retest, follow that label even when your volume estimate is good.
What if my pool is an irregular shape?
Select Kidney / Irregular for a rough estimate, or divide the pool into simpler geometric sections and add their volumes. Construction drawings or metered fill data can be more reliable for highly irregular pools.