Case 1
- Pool shape
- Rectangular
- Length
- 16ft
- Width
- 32ft
- Diameter
- 18ft
- Depth at the shallow end
- 3ft
- Depth at the deep end
- 7ft
19,200 gal · 72,680 L
Open with these valuesPool Volume Calculator
19,200 gal · 72,680 L
Result: 19,200 gal · 72,680 LPick the shape, measure in feet, give both end depths. Rectangles take length × width × average depth × 7.5; round and oval take 5.9, because an ellipse fills only π/4 of its box. A 16 × 32 ft pool sloping from 3 ft to 7 ft holds 19,200 gallons, about 72,700 litres.
The numbers at a glance
Held fixed: Pool shape Rectangular, Length 32.00 ft, Width 16.00 ft, Diameter 18.00 ft, Depth at the shallow end 3.00 ft.
| Depth at the deep end (ft) | Result |
|---|---|
| 0.00 | 5,760 |
| 2.00 | 9,600 |
| 4.00 | 13,440 |
| 6.00 | 17,280 |
| 7.00Your value | 19,200 |
| 8.00 | 21,120 |
| 10.00 | 24,960 |
| 12.00 | 28,800 |
| 14.00 | 32,640 |
Worked examples
Case 2
- Pool shape
- Round
- Length
- 32ft
- Width
- 16ft
- Diameter
- 18ft
- Depth at the shallow end
- 4ft
- Depth at the deep end
- 4ft
7,646 gal · 28,945 L
Open with these valuesCase 3
- Pool shape
- Oval
- Length
- 30ft
- Width
- 11ft
- Diameter
- 18ft
- Depth at the shallow end
- 4ft
- Depth at the deep end
- 4ft
7,788 gal · 29,481 L
Open with these valuesHow it's calculated
gallons = length × width × ((shallow + deep) ÷ 2) × 7.5 — round and oval use 5.9
- StepChoose the shape. It decides which measurements are read and which factor applies.
- StepMeasure in feet, to the waterline — not to the top of the wall.
- StepGive the depth at each end; a flat-bottomed pool takes the same number twice.
- ResultRead the gallons, with litres beside them.
What this number means
Every chemical dose for a pool is quoted per volume, so the volume is the number the rest of the season hangs on. Two things make it more than length times width times depth. The first is shape: a round or oval pool fills only about 79 percent of the rectangle it sits in, which is why the factor drops from 7.5 gallons per cubic foot to 5.9. Using 7.5 on a round pool overstates the water by 27 percent and overdoses everything you add. The second is the floor. Most in-ground pools slope, and the volume follows the average of the shallow and deep ends rather than either one. Measure to the waterline, not the top of the wall — an above-ground pool with a 52 inch wall usually holds about 48 inches of water, and using the wall height inflates the result by roughly a tenth. The 7.5 figure is the industry rounding of 7.481 gallons per cubic foot. It runs about a quarter of a percent high, which is the safe direction: a slightly overstated pool never leads to underdosing.
Measure water, not wall
An above-ground pool with a 52 inch wall is filled to roughly 48 inches. Entering the wall height instead of the water depth adds about 8 percent to every chemical dose.
Round and oval share a factor
A circle is the special case of an ellipse where length equals width, so both use 5.9 gallons per cubic foot. Only the field you fill in changes.
7.5 is a rounding, and a deliberate one
A cubic foot holds 7.481 gallons. The 7.5 used here is the figure the source sheet prints; it runs 0.26 percent high, and erring high never causes underdosing.
Commonly misread
My pool is 4 ft at one end and 8 ft at the other, so I will use 8.
Use the average, 6 ft. The deep end is a small part of the floor, and taking it as the whole overstates the water by a third.
A round pool is close enough to a square one.
It holds about 79 percent as much — π/4 of its bounding box. That is the whole reason the factor is 5.9 rather than 7.5.
Reference table
| Pool | Depth | Gallons |
|---|---|---|
| 15 ft round | 4 ft | 5,300 |
| 18 ft round | 4 ft | 7,600 |
| 24 ft round | 4 ft | 13,600 |
| 15 × 30 ft oval | 4 ft | 10,600 |
| 12 × 24 ft rectangle | 3 ft to 7 ft | 10,800 |
| 16 × 32 ft rectangle | 3 ft to 7 ft | 19,200 |
| 20 × 40 ft rectangle | 3 ft to 7 ft | 30,000 |
Questions
How many gallons is my pool?
Multiply length by width by the average depth, then by 7.5 for a rectangle or 5.9 for a round or oval pool. A 16 × 32 ft pool averaging 5 ft holds 19,200 gallons.
What is the average depth of a pool?
Add the depth at the shallow end to the depth at the deep end and halve it. A pool running 3 ft to 7 ft averages 5 ft.
Why do round pools use 5.9 instead of 7.5?
Because a circle covers only π/4 of the square around it, and 7.5 × π/4 is 5.89. Ovals get the same treatment for the same reason.
How many gallons in a 24 ft round pool?
About 13,600 at four feet of water — 24 × 24 × 4 × 5.9. That is the figure the source chart lists for a 48 inch wall.
How many litres is that?
One US gallon is 3.785 411 784 litres exactly, and the litre figure sits beside the answer. A 19,200 gallon pool is about 72,700 litres.
Does this work for a kidney or freeform pool?
Not directly. Split it into rectangles and ovals, run each through this page, and add the results.
Sources and last check
Information, not professional advice.