Pool volume calculator

Pick your pool's shape, enter its size and depths, and see how many gallons or litres it holds, with a top-down plan and the depth from end to end.

Inputs

Pool shape

Oval is a true ellipse (most above-ground ovals). Oblong has straight sides and round ends.

The longest distance, end to end.

Measured from the water line.

Leave blank for a floor that slopes evenly from end to end.

Pool volume

19,150gal

≈ 72,491 L, at an average depth of 5.0 ft.

Litres
72,491 L
Surface area
512 sq ft
Average depth
5.0 ft
Cubic feet
2,560 cu ft
Water weight
159,344 lb
Your pool from above, and the depth from end to end
512 sq ft32 ft16 ftSide view, depth exaggeratedaverage 5.0 ft3.5 ft6.5 ft

A rectangular pool 32 ft long and 16 ft wide, 3.5 ft deep at the shallow end and 6.5 ft at the deep end, has a surface area of 512 sq ft and an average depth of 5.0 ft. It holds about 19,150 gal (72,491 L) of water.

How it works

Volume is the water’s surface area multiplied by its average depth:

gallons = surface area (sq ft) × average depth (ft) × 7.4805
litres  = surface area (m²) × average depth (m) × 1000

The surface area depends on the shape:

  • Rectangle: length × width.
  • Round: π × radius², or 0.785 × diameter².
  • Oval (true ellipse): 0.785 × length × width. This is where the pool-shop rule “length × width × depth × 5.9” comes from: 7.48 × 0.785 = 5.87.
  • Oblong (straight sides, round ends): (length − width) × width + 0.785 × width².
  • Kidney: 0.45 × (A + B) × length, where A and B are the widths across the two lobes. This is the pool-operator rule the Tulsa Health Department teaches.

For a floor that slopes evenly, the average depth is (shallow + deep) ÷ 2. If there is a flat shallow area and a flat deep area, the calculator averages the whole profile: (shallow × flat shallow length + the middle of the two depths × slope length + deep × flat deep length) ÷ total length.

Worked example

A 16 × 32 ft rectangular pool, 3.5 ft at the shallow end and 6.5 ft at the deep end, sloping evenly:

  • Surface area: 16 × 32 = 512 sq ft
  • Average depth: (3.5 + 6.5) ÷ 2 = 5 ft
  • Volume: 512 × 5 × 7.4805 = 19,150 gallons (72,490 litres), and the water weighs about 159,000 lb.

Now say the same pool has a 12 ft flat shallow area at 3.5 ft, then slopes to 8 ft, with a 6 ft flat area at the deep end. The average depth becomes (3.5 × 12 + 5.75 × 14 + 8 × 6) ÷ 32 = 5.33 ft, and the pool holds 20,410 gallons. Using the simple (3.5 + 8) ÷ 2 = 5.75 ft would have said 22,020, 8% too much.

The same 16 × 32 ft size as an oblong (straight sides, round ends) holds 17,100 gallons, and as a true ellipse 15,040. As a kidney 16 and 18 ft across its lobes, 0.45 × 34 × 32 = 489.6 sq ft, it holds 18,310.

Tips from the pool deck

  • Water line, not the coping. Measure every depth from where the water actually sits.
  • Don’t trust the brochure. An “18 ft round” above-ground pool is 18 ft across the frame; the water can be a few inches narrower.
  • Steps and benches take a little away. Built-in steps, sun shelves and benches hold less water than the pool’s outline suggests. For chemical doses that difference usually doesn’t matter; for a heater or a salt cell it’s a reason to round down, not up.
  • Check it once for real. Next time you refill, note your water meter before and after. That number beats any formula.

FAQ

How many gallons are in my pool?

Multiply the surface area in square feet by the average depth in feet, then by 7.48. A 16 × 32 ft rectangle averaging 5 ft deep is 512 × 5 × 7.48 = about 19,150 gallons. Round pools use 3.14 × radius², ovals 0.785 × length × width, and kidneys 0.45 × (A + B) × length for the area.

Is my oval pool an "oval" or an "oblong"?

Look at the sides. If they curve all the way round, like an egg, pick Oval (a true ellipse; most above-ground ovals). If the long sides are straight with round ends, like a running track, pick Oblong. For a 16 × 32 ft pool the oblong holds about 14% more water.

Why is the average depth not just the middle of the two ends?

It is, when the floor slopes evenly from one end to the other. Most inground pools don't. A long flat shallow area pulls the average toward the shallow depth, and a deep hopper pulls it the other way. Enter the length of each flat part and the calculator averages the real profile.

7.48 or 7.5 gallons per cubic foot?

A cubic foot is exactly 1728 ÷ 231 = 7.4805 US gallons. The Tulsa Health Department's manual uses 7.48; Idaho's manual and many pool shops round to 7.5, which reads about 0.3% high. The calculator uses the exact figure.

How accurate is this for a free-form pool?

The kidney rule is an estimate made for kidney shapes. For an L-shaped pool, split it into two rectangles and add them. For anything else, the most accurate method is a water meter reading or timing how long the pool takes to fill.

Sources

  1. Pool Operators Permit Instruction Manual (section 1, pool and spa calculations), Tulsa Health Department. One cubic foot holds 7.48 gallons; average depth = (shallow + deep) ÷ 2; 40 × 20 × 4 ft = 23,936 gallons; a 24 ft round pool 3.5 ft deep holds 11,837.5 gallons; kidney = (A + B) × L × 0.45 × average depth × 7.48, e.g. 10,987 gallons for 16 + 18 by 32 ft at 3 ft.
  2. How To Calculate Pool Volume, Doheny's. Length × width × average depth × 7.5; a 36 × 12 ft pool, 3 to 9 ft deep, holds 19,440 gallons. Tables of common sizes; the inground "oval" rows match straight sides with round ends, and the above-ground ovals a true ellipse.
  3. Swimming Pool Course Operator's Manual, pool helps and formulas, Idaho Public Health District 5. 1 cubic foot of water = 7.5 gallons (rounded); circle volume = πr² × depth × 7.5.

Formula and sources last checked September 30, 2026. How we test formulas.

  • Pool chemical calculatorHow much chlorine, baking soda, acid, calcium chloride and stabilizer to balance your pool, in order, with before and after gauges for FC, pH, TA, CH and CYA.
  • Pool salt calculatorHow many pounds of salt and how many bags take your saltwater pool from its current ppm to the level your chlorine generator wants, with a ppm meter and bags.
  • Pool heater size & heat-up cost calculatorWhat size pool heater you need in BTU, how long yours takes to heat the pool and what heat-up costs with gas, propane or a heat pump, with a heat-up curve.
  • Hot tub volume calculatorEstimate how many gallons your hot tub or spa holds from its size, for portable acrylic spas, wooden and in-ground tubs, and inflatables.
  • Hot tub chemical calculatorHow much dichlor or chlorine, baking soda, pH down and calcium to balance your hot tub by its size, in order, with before and after meters for spa ranges.
  • Pond liner size & volume calculatorWhat size pond liner you need and how many gallons your pond holds, for rectangular, round, oval and free-form ponds, drawn on the liner.