Pool Volume Calculator

How to calculate pool volume

To calculate pool volume in gallons: multiply length × width × average depth, then multiply by 7.48. Average depth = (shallow depth + deep depth) ÷ 2. For a 16×32 ft pool with 3.5-ft shallow and 5.5-ft deep: 16 × 32 × 4.5 × 7.48 = 17,251 gallons.

1. 1

   Measure pool dimensions

   Measure length, width, shallow end depth, and deep end depth in feet. Measure edge to edge, not tile to tile. For an existing pool, pull the dimensions from the construction drawing when possible.

2. 2

   Calculate average depth

   Average depth = (shallow + deep) ÷ 2. A 3.5-ft shallow end and a 5.5-ft deep end give a 4.5-ft average. Use this average, not the deep end, for the volume calculation.

3. 3

   Multiply length × width × average depth

   For a rectangular pool, that product is the volume in cubic feet. For a 16×32 pool at 4.5 ft average: 16 × 32 × 4.5 = 2,304 ft³. Non-rectangular shapes apply a coefficient — see the formula table below.

4. 4

   Convert cubic feet to gallons

   Multiply cubic feet by 7.48052 for gallons. Multiply by 28.317 for liters. The 7.48052 factor is the NIST Handbook 44 exact conversion — field calculators often round to 7.5, which overestimates by 0.26%.

5. 5

   Apply shape coefficient for non-rectangular pools

   Oval × 0.785 (π/4). Kidney × 0.585 (APSP empirical). Round: use π × r² × depth. L-shaped: split into sub-rectangles and sum. Freeform: use measured surface area × average depth.

Pool volume formulas by shape

Every shape reduces to the same core: surface area × average depth × 7.48052. What changes is how you compute surface area. The table below gives the working formula for each of the six shapes the calculator supports, with the coefficient and its source. The factor 7.48052 gal/ft³ is the exact NIST conversion — field practice often rounds to 7.5, adding about 0.26% to the result.

Rectangular pool volume

Rectangular pools are the highest-demand shape and the baseline for every other formula. Volume equals length × width × average depth × 7.48052. A 16×32 ft pool at 4.5-ft average depth holds 17,251 gallons. Use this shape for any pool whose plan view is a true rectangle, including lap pools.

Oval pool volume

Oval pool volume = L × W × 0.785 × average depth × 7.48052. The 0.785 coefficient is π/4 — the ratio of an ellipse inscribed inside its bounding rectangle. A 15×30 oval at 5-ft uniform depth holds 13,270 gallons, roughly 21% less than a 15×30 rectangle at the same depth.

Kidney-shaped pool volume

Kidney-shaped pool volume = Length × Width × 0.585 × Average Depth × 7.48. The 0.585 coefficient accounts for the kidney shape's curved indentation, which reduces total surface area by about 41.5% compared to the bounding rectangle. Source: APSP Pool Volume Guidelines.

L-shaped pool volume

Split the L-shape into two rectangles along its inside corner. Calculate each rectangle's volume (L × W × D_avg × 7.48052), then sum. A 20×12 section plus a 10×10 section at 5-ft average depth totals 12,716 gallons. Do not use the bounding rectangle — that overestimates volume by the area of the missing corner.

Round pool volume

Round pool volume = π × radius² × depth × 7.48052. Radius = diameter ÷ 2. Round pools — typical above-ground and spool designs — use a single uniform depth rather than shallow/deep ends. An 18-ft-diameter round pool at 4-ft uniform depth holds 7,620 gallons.

Freeform pool volume

Freeform pools have no closed-form formula. Instead, pull the water surface area (sq ft) from the pool architect's plan drawing — most plan sets label it as “Water Surface Area” or “Pool Area.” Then: Volume = Surface Area × Average Depth × 7.48052. A 400 sq ft freeform at 4.5-ft average depth holds 13,465 gallons.

How long does it take to fill a pool?

To calculate pool fill time, divide pool volume (gallons) by your water source flow rate (GPH). A standard 5/8-inch garden hose delivers ~540 GPH. A 20,000-gallon pool takes about 37 hours. Adjust for a 3/4-inch hose (~780 GPH) or bulk water delivery.

Fill time is a real line item on pool construction schedules, not a side note. Pool inspection usually cannot happen until the pool is full and clear, so fill time sits on the critical path to substantial completion. Plan for it the same way you plan any other construction activity — with a start date, a duration, and a dependency on the water source.

Fill time by water source

Field note: scheduling the pool fill

Use the fill time panel in the calculator above to size the water source against your pool volume. For projects where water cost is a meaningful line item, the pool cost calculator can translate gallons into a dollar figure at your local utility rate.

Pool volume reference — common pool sizes

A 12×24 rectangular pool with a 5-foot average depth holds approximately 10,771 gallons (12 × 24 × 5 × 7.48052). With a 4-foot average depth that figure drops to 8,617 gallons. Exact volume depends on your actual depth profile — the reference table covers the 12 most common residential configurations.

How to size a pool pump based on volume

Required pump flow rate (GPM) = Pool Volume ÷ Turnover Time (hours) ÷ 60. Residential pools target 6-hour turnover. For a 20,000-gallon pool: 20,000 ÷ 6 ÷ 60 = 55.6 GPM minimum. Present this figure to your mechanical engineer for final pump selection.

Turnover time is the number of hours required to filter the full pool volume once. APSP-7 sets 6 hours as the residential standard; the Model Aquatic Health Code (MAHC) sets 4 hours for commercial pools, with 30 minutes for interactive splash pads. Dividing by 60 converts the hourly volume into gallons per minute — the spec sheet unit for every pool pump on the market.

Field note: pump spec for new construction

New pool startup: chemical dosing by shell type

Startup chemistry is a one-time construction activity tied to the pool's shell material — not the same as weekly maintenance dosing. The goal is to establish sanitizer residual before the pool is handed over to the owner, without damaging a fresh pool surface. The following sub-sections cover the three dominant residential shell types: new plaster, vinyl liner, and fiberglass. Target figures cite NSF/ANSI 50 and CDC Healthy Swimming guidance; always verify with the pool startup contractor's specification for your project.

New plaster (marcite)

For new plaster pool startup, the standard initial dose is approximately 1 lb of calcium hypochlorite (65% available chlorine) per 10,000 gallons, targeting 10 ppm free chlorine for the first 24 hours. New plaster continuously releases calcium hydroxide into the water for 28–30 days, driving pH upward — monitor pH daily and adjust with muriatic acid to hold a 7.2–7.6 range. Calcium hardness will also climb during this window; expect 50–100 ppm of upward drift from the plaster alone.

Vinyl liner

Vinyl liner startup runs gentler than plaster — target 3–5 ppm free chlorine for opening, not the 10 ppm shock dose used on new plaster. Calcium hypochlorite or sodium dichlor both work; a half-pound of 65% cal-hypo per 10,000 gallons generally holds vinyl in range. Do not exceed 5 ppm on a new liner; higher concentrations can fade the printed pattern and accelerate liner aging at the waterline.

Fiberglass

Fiberglass shells are pH-sensitive at startup. Target 3 ppm free chlorine with careful pH control at 7.4–7.6. A half-pound of 65% cal-hypo per 10,000 gallons is the working baseline. Confirm the shock tolerance with the shell manufacturer before dosing — some resin formulations require liquid sodium hypochlorite only. Do not use trichlor tablets on startup; the low pH of trichlor etches a fresh fiberglass gelcoat.

Pool volume for permit applications

Most building departments require pool volume in gallons on the permit application, alongside overall plan dimensions and deep-end depth. The figure flows downstream: water utility connection sizing, fire-department bulk-fill approval (where required), electrical service sizing for pump and heater, and mechanical equipment schedules all reference the permit volume. Calculate it early at schematic design using the architect's plan dimensions — field adjustment at substantial completion is typically ±5%.

Field note: volume on the permit application

Pool volume conversion: gallons, cubic feet, and liters

US contractors work in gallons; engineers and anyone outside the US work in cubic meters or liters. The calculator above toggles between all three output units. Conversion factors come from NIST Handbook 44: 1 cubic foot equals 7.48052 US gallons; 1 US gallon equals 3.78541 liters; 1 cubic meter equals 264.172 US gallons. The common field approximation of 7.5 gal/ft³ overestimates by 0.26% — about 52 gallons on a 20,000-gallon pool. Use the exact value for permit documents.

Need cubic yardage for a different material? The cubic yards calculator handles any rectangular or custom volume in cubic yards, feet, or meters.

Frequently asked questions