Gallons in a 12 × 18 ft oval pool, by wall height
Above-ground pools are normally filled about 6 inches below the top of the wall. The usual rule treats the pool as a true oval (an ellipse), with a surface of 170 sq ft. Many oval above-ground pools have straight sides and round ends instead, which holds about 9% more water, so both are shown. Measure your pool to see which it is.
| Wall height | Typical water depth | Gallons (true oval) | Gallons (straight sides) |
|---|---|---|---|
| 48 in wall | 42 in | 4,442 | 4,846 |
| 52 in wall | 46 in | 4,865 | 5,308 |
| 54 in wall | 48 in | 5,076 | 5,538 |
By water depth
The fill time is for a garden hose delivering 9 gallons per minute, and the figures are for a true oval.
| Water depth | Gallons | Liters | Hose fill time |
|---|---|---|---|
| 3.5 ft | 4,442 | 16,813 | 8.2 hrs |
| 4 ft | 5,076 | 19,215 | 9.4 hrs |
| 4.5 ft | 5,711 | 21,617 | 10.6 hrs |
Pool chemical doses are given per number of gallons, and the pump and filter are sized to circulate the volume. Use the pool volume calculator with your own measurements, see the round pool and rectangular pool charts, or read how to calculate pool volume.
Water weight, pump size and fill cost
At 5,076 gallons, this pool holds about 42,335 lb of water (21.2 tons). That is a lot of weight on one patch of ground, which is why the base must be level and well compacted before you fill it.
To turn the whole volume over through the filter in 8 hours, the pump and filter need to move at least 10.6 gallons per minute (14.1 GPM for a 6-hour turnover). If a chemical label gives a dose per 10,000 gallons, multiply it by 0.51 for this pool.
| Water price per 1,000 gal | Cost to fill |
|---|---|
| $4 | $20 |
| $6 | $30 |
| $8 | $41 |
Water prices vary a lot, and some utilities charge a separate sewer rate that does not apply to a pool. Check your own bill.
Want to change anything else? The calculator above is the full Pool Volume Calculator: edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How many gallons in a 12x18 oval pool?
About 5,076 gallons at a 4 ft water depth. A pool with 52 in walls filled to about 46 in holds roughly 4,865 gallons. If your pool has long straight sides with round ends, it holds more: about 5,308 gallons at 46 in.
How do you work out the gallons in an oval pool?
Multiply length × width × average water depth, all in feet, by 5.88. That is π ÷ 4 for the oval shape times 7.48 gallons in a cubic foot, and it is often rounded to 5.9. For a 12 × 18 ft pool at 4 ft deep: 12 × 18 × 4 × 5.88 ≈ 5,076 gallons.
How long does it take to fill a 12x18 oval pool with a hose?
At 9 gallons per minute, filling to 4 ft takes about 9.4 hours (0.4 days). For a big pool a water delivery truck can be quicker. Time your own hose: fill a 5 gallon bucket and divide.
Related sizes and guides
Related sizes
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.