The round pool formula
diameter × diameter × average depth × 5.9 = gallons
Feet and gallons. The exact version is π × radius² × depth × 7.48 gallons per cubic foot; since π ÷ 4 × 7.48 is 5.875, the trade rounds to 5.9, and so does this calculator. A 24 ft round pool with 4 ft of water: 24 × 24 × 4 × 5.9 = 13,590 gallons. In litres multiply by 3.785, which is about 51,500.
Round pool gallons by diameter and depth
| Diameter | 3.5 ft of water | 4 ft of water | 4.5 ft of water | 5 ft of water |
|---|---|---|---|---|
| 12 ft | 2,970 | 3,400 | 3,820 | 4,250 |
| 15 ft | 4,650 | 5,310 | 5,970 | 6,640 |
| 18 ft | 6,690 | 7,650 | 8,600 | 9,560 |
| 21 ft | 9,110 | 10,410 | 11,710 | 13,010 |
| 24 ft | 11,890 | 13,590 | 15,290 | 16,990 |
| 27 ft | 15,050 | 17,200 | 19,350 | 21,510 |
| 30 ft | 18,590 | 21,240 | 23,890 | 26,550 |
| 33 ft | 22,490 | 25,700 | 28,910 | 32,130 |
How to measure
Measure across the pool through the centre, at the water line, in feet. Take the depth from the water line to the floor. An above-ground pool with a 52 in wall is normally filled to about 4 ft. If the floor slopes, average the deepest and shallowest points. For standard above-ground sizes with their wall heights use the above ground pool volume calculator; oval, kidney and rectangle pools are on the pool volume calculator.
Next step: with the gallons saved, the pool chlorine calculator gives the dose in product sizes.
Factor 5.9 = π ÷ 4 × 7.48 gallons per cubic foot, as used in the pool-trade capacity charts. Read October 18, 2026.
Frequently asked questions
How do you find the volume of a circular pool?
Diameter × diameter × average depth × 5.9 gives gallons, with all lengths in feet. The 5.9 is π ÷ 4 × 7.48. A 24 ft round pool with 4 ft of water holds 24 × 24 × 4 × 5.9 = 13,590 gallons.
Is a round pool better than a rectangle?
A round pool holds more water for the same perimeter, is cheaper to build above ground and has no corners where debris sits. A rectangle suits laps and covers. For dosing and heating the shape does not matter, only the gallons.
What is the volume of a 21 ft round pool in litres and cubic metres?
At 4 ft of water about 10,410 gallons, which is 39,400 litres or 39.4 cubic metres. Each extra foot of depth adds about 2,600 gallons (9,850 litres), and each foot less takes the same away.
What size round pool holds 10,000 gallons?
About 20.6 ft across with 4 ft of water. In practice a 21 ft round pool filled to 4 ft holds 10,410 gallons, and a 20 ft round pool filled to 4.5 ft holds 10,620. A 22 ft pool holds 10,000 at 3.5 ft.
Where do I measure a round pool for the calculator?
Measure the diameter across the water at the widest point, through the centre, in feet. Measure the depth from the water line to the floor, at the deep end too if it slopes. Wall height is not water depth.