Assuming common shapes and depths, this is a chart. Otherwise, take it a guess, or ask our water lab technician to re-figure it during your following water test.

Round steel Pools – Gallons

Size48″52″54″
12′3,5003,8004,000
15′5,3005,7005,900
18′7,6008,2008,500
20′9,40010,00010,400
21′10,00011,00011,500
24′13,70014,60015,000
27′15,90016,80017,400
28′18,50020,50021,500
30′19,00021,00022,000
33′25,00027,50028,500

Round Blow-up Pools – Gallons

DiameterHeightGallons
8′30″640
10′30″1000
12′30″1500
12′36″1800
15′36″2800
15′42″3300
15′48″3750
18′42″4800
18′48″5500
18′52″6000

Oval Pools – Gallons

Size48″52″54″
11’ x 18½’6,0006,6006,800
11’ x 25’8,5009,2009,500
12’ x 17’6,0006,6006,800
12’ x 24’8,5009,5009,800
15’ x 25’9,50010,00010,600
15’ x 26’10,20011,00011,400
15’ x 30’13,70014,80015,400
18’ x 33’17,50018,90019,600
18’ x 38’19,50021,00022,000
18’ x 40’20,50022,00022,900

Rectangular Inground Pools – Gallons

Size48″ Shallow to 96″ Deep end
12’ x 24’10,000
16’ x 32’20,000
18’ x 36’25,000
20’ x 40’30,000
24’ x 44’45,000
25’ x 50’50,000

To calculate various other sizes and also shapes; all measurements are in feet:

Round:Diameter x diameter x mean depth x 5.9
or
Round:Radius x radius x mean depth x 23.6
Rectangle:Length x broad x median depth x 7.5
Oval:Length x broad x mean depth x 6.6
Free Form:Surface area (square feet) x median depth x 7.5
Blow-up Pools:Contact the manufacturer since the walls space not vertical and also the collars impact depth, over there is no formula