Pool Volume Calculator: How Many Gallons Is My Pool? (2026)

Pool volume in gallons: rectangular, round, and oval formulas. Average depth calculation, chemical dosing per 10,000 gallons, and pump turnover rate.

Most pool owners treat by guesswork. A scoop of shock here, a tablet there, and one eye on the color of the water. The problem is not neglect. Every chemical dose on every package label is specified per 10,000 gallons, and if you do not know how many gallons your pool holds, you cannot dose correctly for any of them. Undershoot the volume by 30%, and you're swimming in undertreated water regardless of how often you add chemicals. Overshoot it, and you're wasting money on unnecessary product.

The Pool Volume Calculator takes your pool's shape and dimensions and returns gallons and liters in one step. This guide covers the formula for each pool shape, how average depth works, what the gallon count means for chemical dosing and salt treatment, reference figures for common pool sizes, and how pool volume drives pump sizing and filter selection.

How to Calculate Pool Volume in Gallons: Three Formulas for Three Shapes

Pool volume is always calculated in cubic feet first, then converted to gallons using a fixed factor. The conversion is:

1 cubic foot = 7.48052 US gallons

That factor comes from the mathematical definitions: 1 US gallon = 231 cubic inches, and 1 cubic foot = 1,728 cubic inches. Dividing 1,728 by 231 gives 7.48052. Some guides round this to 7.5, which overstates volume by about 0.26%. On a 20,000-gallon pool that adds roughly 260 gallons, a meaningful error when calculating salt dosing.

Rectangular pool:

Cubic feet = Length (ft) × Width (ft) × Average Depth (ft)
Gallons    = Cubic feet × 7.48052

Round pool:

Cubic feet = π × Radius² × Average Depth (ft)
Gallons    = Cubic feet × 7.48052

Radius = Diameter ÷ 2. For an 18-foot diameter pool, Radius = 9.

Oval pool:

Cubic feet = π × (Length ÷ 2) × (Width ÷ 2) × Average Depth (ft)
Gallons    = Cubic feet × 7.48052

Average depth for pools with a sloped bottom:

Most residential in-ground pools have a shallow end and a deep end connected by a gradual slope. Average depth is not the depth at the midpoint of the slope. It is:

Average Depth = (Shallow End Depth + Deep End Depth) ÷ 2

A pool with a 3.5-foot shallow end and a 7.5-foot deep end has an average depth of (3.5 + 7.5) ÷ 2 = 5.5 feet.

Worked example, rectangular:

A pool measures 16 feet wide by 32 feet long. Shallow end is 3 feet, deep end is 7 feet.

Average Depth = (3 + 7) ÷ 2 = 5 ft
Cubic feet    = 16 × 32 × 5 = 2,560 cu ft
Gallons       = 2,560 × 7.48052 = 19,150 gal

Worked example, round:

An above-ground round pool is 18 feet in diameter with a constant depth of 4 feet.

Radius     = 18 ÷ 2 = 9 ft
Cubic feet = π × 9² × 4 = 3.14159 × 81 × 4 = 1,017.9 cu ft
Gallons    = 1,017.9 × 7.48052 = 7,615 gal

Worked example, oval:

An oval pool is 12 feet wide by 20 feet long with a constant depth of 4 feet.

Cubic feet = π × (20 ÷ 2) × (12 ÷ 2) × 4
           = π × 10 × 6 × 4
           = 753.98 cu ft
Gallons    = 753.98 × 7.48052 = 5,640 gal

Pool Volume and Chemical Dosing: The Math Behind Every Treatment

Chemical dosing is where pool volume stops being abstract and starts directly affecting water quality and cost. Every pool treatment product specifies its dose per 10,000 gallons. That is the reference unit across the industry.

Your multiplier for any chemical:

Multiplier = Pool gallons ÷ 10,000

For a 15,000-gallon pool, the multiplier is 1.5. For a 22,000-gallon pool, it is 2.2. Every package dose gets multiplied by this number before you add it to the water.

The following table shows treatment amounts at common pool volumes for reference. Always read the specific product label since formulations and concentrations differ by brand.

Salt dosing for saltwater pools follows the same per-gallon logic but uses parts per million (ppm) rather than a fixed package amount. Most saltwater chlorine generators target 3,200 ppm. If your pool is currently at 500 ppm and you need to reach 3,200, the salt required depends entirely on how many gallons you are treating. The Pool Salt Calculator takes your pool gallons, current ppm, and target ppm and returns the exact pounds of salt needed and the bag count for 40-pound or 50-pound bags. It is the most direct downstream use of a precise volume figure.

The chemistry failures that look like stubborn algae or persistent cloudiness after repeated chemical additions are frequently a volume underestimate. A pool owner adds what they believe is 1.5 lbs of shock for a 15,000-gallon pool. If the pool is actually 20,000 gallons, that dose is 75% of what the water needs. Recalculating from actual measured dimensions often reveals the pool is larger than assumed.

Rectangular Pool Gallons: Reference Figures for Common Dimensions

The following table provides gallon counts for common residential rectangular pool dimensions at three average depths. Use these for a quick reference or dosing check when the calculator is not available.

Calculation check: 16 × 32 × 5 × 7.48052 = 19,150 gallons.

One thing this table cannot capture is your pool's actual average depth, which depends on your specific shallow-to-deep gradient. The formula applied to your measured dimensions will always be more accurate than a table lookup. Measure both the shallow end and the deep end directly rather than relying on the original installer's specifications, which sometimes reflect the planned depth rather than the finished result.

Pool construction projects often run parallel material estimates. A poured concrete pool deck, coping, or retaining wall surround requires its own calculation. The Concrete Bag Calculator estimates the number of bags needed based on the surface area, slab thickness, and concrete mix, which is useful when planning the hardscape around a new or resurfaced pool.

Round and Oval Pools: Volume for Curved Shapes

Round and oval pools are almost entirely above-ground installations in residential settings. Because they have a constant depth rather than a sloped bottom, the average depth calculation is simpler: use the actual water depth, not the wall height. Most above-ground pools are filled to 4 to 6 inches below the rim, so a 48-inch (4-foot) wall pool holds water at roughly 42 to 44 inches.

For dosing purposes, using the full rated depth produces a slight safety margin. You treat at a fractionally higher dose than strictly needed, which is preferable to underdosing.

Round pool gallons by diameter:

The following table shows gallons at two common wall heights for standard above-ground round pool diameters.

Calculation check for 24-ft round at 4 ft depth: π × 12² × 4 × 7.48052 = 13,572 gallons. Minor variation from rounding in the table.

Oval pool calculation:

An oval pool 12 feet wide and 24 feet long at 4 feet depth:

Cubic feet = π × (24 ÷ 2) × (12 ÷ 2) × 4
           = π × 12 × 6 × 4
           = 904.8 cu ft
Gallons    = 904.8 × 7.48052 = 6,768 gal

Round and oval above-ground pools are frequently paired with a surrounding wood or composite deck. Estimating materials for the ring-shaped area between the pool edge and the outer deck boundary requires calculating the deck's total square footage minus the circular pool footprint. The Square Footage Calculator handles composite areas including the annular ring shape you get when a circular pool sits inside a square or rectangular deck frame.

Pump Sizing and Turnover Rate: What Pool Volume Determines

Pump sizing is the application of pool volume that has the largest long-term equipment and energy cost implication. An undersized pump cannot complete the required turnover cycle, leaving circulation dead zones where algae establish. An oversized pump moves water faster than the filter processes it effectively and runs at higher electricity cost without water quality benefit.

The residential standard is one full water turnover every 8 hours. Some county health codes specify 6 hours; the common industry target is 8.

Required pump rate (GPH) = Pool gallons ÷ 8
Required pump rate (GPM) = Pool gallons ÷ 480

For a 20,000-gallon pool:

GPH = 20,000 ÷ 8 = 2,500 GPH minimum
GPM = 20,000 ÷ 480 = 41.7 GPM minimum

Pump capacity ratings appear in GPM at a specific head pressure. As your plumbing adds more feet of pipe, elbows, valves, and filter resistance, the effective GPM drops. Select a pump that meets or slightly exceeds the required GPM at your system's operating head pressure. Sizing up by 10% to 15% to account for increasing filter restriction over a season is reasonable. Sizing up by 50% or more wastes electricity without improving water quality or safety.

Filter sizing and sand media:

Sand filters and cartridge filters are rated by pool volume. Sand filter media requires replacement every 5 to 7 years on residential pools. When replacing filter sand, the volume of new media needed depends on the tank diameter and the required sand bed depth, typically 19 to 24 inches for residential filter tanks. The Sand Calculator handles the volume and weight calculation for cylindrical containers, which maps directly to estimating replacement sand for a filter tank when you know the tank diameter and required fill depth.

Heater sizing also derives from pool volume, though the calculation involves surface area and desired temperature rise rather than gallons directly. For heated pools, BTU output requirements scale with volume, and manufacturers provide sizing tables by gallon range. The pump sizing calculation is always the first step because it establishes the circulation rate the heater must serve.