Gallons in a 18 × 36 ft pool, by average depth
For a pool with a sloping floor, find the average depth first: (shallow end + deep end) ÷ 2. The surface area is 648 ft². The fill time is for a hose delivering 9 gallons per minute.
| Average depth | Gallons | Liters | Hose fill time |
|---|---|---|---|
| 3.5 ft | 16,966 | 64,223 | 31.4 hrs |
| 4 ft | 19,390 | 73,397 | 35.9 hrs |
| 4.5 ft | 21,813 | 82,572 | 40.4 hrs |
| 5 ft | 24,237 | 91,747 | 44.9 hrs |
| 5.5 ft | 26,661 | 100,921 | 49.4 hrs |
| 6 ft | 29,084 | 110,096 | 53.9 hrs |
Why you need the number
Pool chemical doses are given per number of gallons, and pumps, filters and heaters are sized to the volume. Measure the actual water depth in your own pool and follow the label on any product you add.
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 18x36 pool?
It depends on the average depth: about 19,390 gallons at 4 ft, 24,237 at 5 ft and 29,084 at 6 ft. For a sloping bottom, use the average of the shallow and deep ends.
How do I find the average depth of a 18x36 pool?
Add the depth at the shallow end to the depth at the deep end and divide by two. A pool that is 3½ ft at one end and 8 ft at the other averages 5¾ ft, which holds 27,872 gallons at this size.
How long to fill a 18x36 pool with a hose?
At 9 gallons per minute, a 18x36 pool with a 5 ft average depth takes about 45 hours (1.9 days). Many owners have water delivered for pools this size.
Related sizes and guides
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.