Everyday Life · Practical Life · Home & DIY
Pool Volume Calculator
Calculate the total water volume of a swimming pool based on its shape, dimensions, and depth.
Calculator
Formula
V is the pool volume in US gallons. L is the length in feet, W is the width in feet, r is the radius in feet (diameter / 2), and D_avg is the average depth in feet (shallow end depth plus deep end depth divided by 2). The constant 7.481 converts cubic feet to US gallons. For rectangular pools, multiply length × width × average depth × 7.481. For round pools, use π × r² × average depth × 7.481. For oval pools, use π × (L/2) × (W/2) × average depth × 7.481.
Source: Pool & Hot Tub Alliance (PHTA) — Standard Pool Volume Calculation Methods
How it works
Swimming pool volume is calculated by multiplying the pool's surface area by its average depth. Because most pools have a sloped floor transitioning from a shallow end to a deep end, the average depth is used rather than either extreme alone. The average depth is simply the shallow end depth plus the deep end depth divided by two. The result in cubic feet is then multiplied by 7.481 to convert to US gallons, or by 28.317 to convert to liters.
The formula varies slightly by pool shape. For a rectangular pool, surface area is length times width. For a round (circular) pool, the surface area is π times the radius squared, where the radius is half the diameter. For an oval pool, surface area is π times half the length times half the width — essentially the formula for an ellipse. In every case, the surface area is then multiplied by average depth and the appropriate unit conversion factor. This calculator also estimates your filter turnover time, assuming a common pump flow rate of 3,000 gallons per hour (GPH); you can scale this proportionally for your actual pump rating.
These calculations are used by pool service professionals to determine chemical dosing (chlorine, pH adjusters, algaecide), pump sizing for adequate water circulation, and filter run times. Water utility companies also use pool volume data for billing purposes when pools are filled using metered connections. Accurate volume knowledge prevents both under-treatment (leading to algae and bacterial growth) and over-treatment (wasting chemicals and potentially irritating swimmers).
Worked example
Suppose you have a rectangular pool that is 32 feet long, 16 feet wide, with a shallow end of 3.5 feet and a deep end of 8 feet.
Step 1 — Average Depth:
(3.5 + 8) ÷ 2 = 5.75 feet
Step 2 — Volume in Cubic Feet:
32 × 16 × 5.75 = 2,944 ft³
Step 3 — Convert to US Gallons:
2,944 × 7.481 = 22,023 gallons
Step 4 — Convert to Liters:
2,944 × 28.317 = 83,365 liters
Step 5 — Filter Turnover Time (at 3,000 GPH pump):
22,023 ÷ 3,000 = 7.3 hours to cycle all the water once through the filter.
This tells you the pump should run at least 7–8 hours per day for adequate filtration. For chemical dosing, you would use the 22,023-gallon figure when following dosage instructions on chlorine, algaecide, or balancing chemicals.
Limitations & notes
This calculator assumes a simple linear slope between the shallow and deep ends, which is accurate for most standard residential pools. Pools with complex shapes — such as L-shaped, kidney-shaped, or freeform pools — should be broken into simpler sections and calculated separately before adding totals. The oval formula treats the pool as a perfect ellipse; pools that are only approximately oval may have slight volume discrepancies. The turnover time estimate assumes a constant pump flow rate of exactly 3,000 GPH; adjust proportionally for your actual pump's rated flow rate, and account for head pressure losses in real installations. This tool uses US gallons; note that Imperial (UK) gallons are approximately 20% larger than US gallons. Always verify chemical dosing with your pool service professional, as water chemistry also depends on factors like bather load, sunlight exposure, and water source chemistry.
Frequently asked questions
How many gallons is a typical backyard swimming pool?
Most residential in-ground pools hold between 15,000 and 30,000 US gallons, depending on size and depth. A common 16×32 ft pool with an average depth of 5.5 feet holds approximately 21,000 gallons. Above-ground pools are typically smaller, ranging from 2,500 to 15,000 gallons.
Why do I need to know my pool's volume?
Pool volume is the foundation for virtually every pool maintenance decision. Chemical dosages for chlorine, pH balancers, algaecide, and shock treatments are all specified per 10,000 gallons. Knowing your exact volume prevents costly over-treatment or dangerous under-treatment. It also helps you size your pump and filter correctly and estimate water fill costs.
How do I calculate pool volume for a round above-ground pool?
For a round pool, measure the diameter (not the radius) and enter it in the Length field, then use the Round shape option. The calculator uses the formula V = π × (diameter/2)² × average depth × 7.481. For a flat-bottomed above-ground pool, simply enter the same value for both shallow and deep end depth.
What is pool turnover rate and why does it matter?
Turnover rate is how long it takes your pump and filter to circulate the entire pool volume once. Most health and pool industry standards recommend a full turnover every 6–8 hours, meaning your pump should run at least 8 hours per day. An undersized pump that takes 12+ hours per turnover can lead to poor filtration and water clarity issues.
How do I calculate volume for an L-shaped or freeform pool?
Divide the pool into two or more simple rectangular, round, or oval sections. Calculate the volume of each section separately using this calculator, then add them together for the total pool volume. For highly irregular freeform pools, your pool builder should have the exact volume documented from the construction specifications.
Last updated: 2025-01-15 · Formula verified against primary sources.