You don't say how deep the pool is and whether you're using US or UK gallons. However... One cubic foot contains approximately 7.5 US gallons, or 6.25 UK gallons, so if you multiply 10 x 3 x (pool depth) by either of the above you will get the approximate gallon count.
18,000
Between 300 - 500 US Gallons in most 3-6 seaters.
This cylinder will hold up to 3,760.11 gallons of water.
141.06 gallons
A 15 cubic foot tank will hold a maximum of about 112.2 gallons of water.
There are 13,536 gallons in a 24 foot diameter pool that has 4 feet of water. Not true for a pool that is 4 feet in height. This would hold less than 4 feet of water.
About 14,351 US gallons of water.
700 gallons
30 feet X 15 feet X 4 feet would be (30 X 15 X 4) = 1,800 cubic feet of water.1 cubic foot of water = 7.48051948 US gallonsso 1,800 X 7.48051948 = 13,464.935064 gallons.
17,000 gallons
0.212 331 gallons per foot.
A pool this size will hold about 21,544 gallons of water.