What an 18 ft round pool needs (7,650 gallons, 52 in wall)
| What | Amount | Assumes |
|---|---|---|
| Salt for a salt chlorinator | 200 lb (6 bags of 40 lb) | fresh water to 3,200 ppm |
| Chlorine to raise FC 1 ppm | 8.2 fl oz | 12.5 % liquid chlorine |
| Pump flow | 16 gpm | whole pool through the filter in 8 hours |
| Fill time | about 14 hours | one garden hose at 9 gpm |
| Sand base | 1.6 cu yd (85 bags of 50 lb) | 2 in under the 18 ft footprint |
| Evaporation | about 40 gal a day | 254 sq ft of water, 0.25 in a day |
Gallons by wall height
| Wall | Water depth | Gallons | Litres | Salt to 3,200 ppm |
|---|---|---|---|---|
| 48 in | 3.5 ft | 6,690 | 25,300 | 180 lb |
| 52 in | 4 ft | 7,650 | 28,900 | 200 lb |
| 54 in | 4.5 ft | 8,600 | 32,600 | 230 lb |
Round pool: diameter × diameter × water depth × 5.9. For an 18 ft round pool with 4 ft of water: 18 × 18 × 4 × 5.9 = 7,646 gallons. 5.9 is π ÷ 4 × 7.48 gallons per cubic foot, rounded as the pool trade does, so these figures match the capacity charts pool stores print. The charts assume a water level for each wall height; if yours differs, use the water depth table below.
Gallons by water depth
| Water depth | Gallons | Litres |
|---|---|---|
| 36 in (3.00 ft) | 5,730 | 21,700 |
| 39 in (3.25 ft) | 6,210 | 23,500 |
| 42 in (3.50 ft) | 6,690 | 25,300 |
| 45 in (3.75 ft) | 7,170 | 27,100 |
| 48 in (4.00 ft) | 7,650 | 28,900 |
| 51 in (4.25 ft) | 8,120 | 30,800 |
| 54 in (4.50 ft) | 8,600 | 32,600 |
Measure from the floor to the waterline in a few places and use the average. Your level is not in the table? Open this pool in the pool volume calculator and type your depth; the round pool volume calculator also takes the depth in inches.
Other sizes
The pool sizes in gallons charts list every common round, oval and inground size, and the above ground pool volume calculator works out any other above-ground pool from its wall height.
Other sizes with their own page, each with its salt, chlorine, pump flow and fill time: 24 ft round pool, 27 ft round pool, 18x33 oval pool and 16x32 inground pool.
Frequently asked questions
How many gallons does an 18 foot by 48 inch pool hold?
A 48 in wall is filled to about 3.5 ft of water, so the pool holds 6,690 gallons (about 25,300 litres). Filled to 4 ft, as with a 52 in wall, it holds 7,650 gallons.
How many gallons is an 18 ft round pool that is 4.5 ft deep?
8,600 gallons, about 32,600 litres. 4.5 ft is the water level the capacity charts assume for a 54 in wall. Every 3 inches of water adds or removes about 480 gallons.
How much chlorine does an 18 ft round pool need?
Raising free chlorine by 1 ppm in 7,650 gallons (52 in wall) takes 8.2 fl oz of 12.5 % liquid chlorine; 3 ppm takes 25 fl oz. How high to go depends on your stabilizer (CYA) level, which the pool chlorine calculator works out.
How much salt does an 18 ft round pool need?
From fresh water to 3,200 ppm: 200 lb at a 52 in wall (6 bags of 40 lb), 180 lb at 48 in and 230 lb at 54 in. Check your chlorinator's target first and add in steps.
How many litres is an 18 ft round pool?
25,300 litres with a 48 in wall, 28,900 with a 52 in wall and 32,600 with a 54 in wall, at the water levels the capacity charts use (3.5, 4 and 4.5 ft). One US gallon is 3.785 litres.
Water depth per wall height (48 in = 3.5 ft, 52 in = 4 ft, 54 in = 4.5 ft): pool-trade capacity charts (Swimming Pool Discounters, "Gallons of Water per Pool Size Chart"; Energy Kinetics, "Standard Pool Above Ground Pool Sizes"), read October 18, 2026. Salt: 1 lb per 10,000 gal ≈ 12 ppm and liquid chlorine 10.7 fl oz per ppm per 10,000 gal (Trouble Free Pool, Pool School; product labels), read October 18, 2026. Sand: 2 in base, 50 lb bag = 0.5 cu ft (Royal Swimming Pools; Quikrete All-Purpose Sand), read October 23, 2026. Hose flow, turnover hours and evaporation rate are example inputs: the linked calculators take your own. Gallons rounded to the nearest 10, litres to the nearest 100.