Calculate pool gallons from your pool shape, dimensions, and water depth. Pick how you want to measure depth, enter your numbers, and the calculator returns the water volume in gallons, liters, or cubic meters. You can also solve for how long the pool takes to fill from a known volume and a flow rate.
Pool Gallon Formula
The volume of any pool is its surface area multiplied by the average water depth. Multiplying cubic feet by 7.48 converts the result into US gallons, since one cubic foot of water holds 7.48 gallons.
Gallons = Area * AvgDepth * 7.48
When you enter a shallow depth and a deep depth instead of one average, the average depth is the mean of the two:
AvgDepth = (Shallow + Deep) / 2
The surface area depends on the shape you select:
Rectangle: Area = Length * Width
Circle: Area = pi * (Diameter / 2)^2
Oval: Area = pi / 4 * Length * Width
Kidney: Area = (WidthA + WidthB) * Length * 0.45
Triangle: Area = Base * Height / 2
When you solve for fill time, the calculator divides the volume by the flow rate of your hose or pump:
FillTime = Volume / FlowRate
- Gallons = pool water volume in US gallons
- Area = surface area of the pool in square feet
- AvgDepth = average water depth in feet
- Shallow = depth at the shallow end
- Deep = depth at the deep end
- Length, Width = the two main horizontal dimensions
- Diameter = width of a round pool across the center
- WidthA, WidthB = the two different widths of a kidney pool
- Base, Height = the base and perpendicular height of a triangular pool
- 7.48 = US gallons per cubic foot
- Volume = known pool volume used for the fill time mode
- FlowRate = water delivery rate of your source
The shape selector sets which area formula is used and shows only the inputs that shape needs. The depth input lets you give one average depth or separate shallow and deep depths, which the calculator averages for you. The unit selectors convert your entries to a common base before the math runs, so you can mix measurement habits and still read the answer in gallons, liters, or cubic meters. The fill time mode skips the geometry and works straight from a volume and a flow rate.
Typical Pool Sizes and Volumes
These figures assume an average depth of about 5 feet and are useful for a quick sanity check against your own result.
| Pool size and shape | Approximate gallons |
|---|---|
| 12 ft round | 3,400 |
| 24 ft round | 13,500 |
| 15 x 30 ft rectangle | 16,800 |
| 20 x 40 ft rectangle | 29,900 |
| 16 x 32 ft oval | 15,000 |
To convert a result between units, use these factors.
| Conversion | Value |
|---|---|
| 1 cubic foot | 7.48 US gallons |
| 1 US gallon | 3.785 liters |
| 1 cubic meter | 264.2 US gallons |
Example Calculations
A rectangular pool is 16 feet wide and 32 feet long, with a shallow end of 3 feet and a deep end of 8 feet. The average depth is (3 + 8) / 2 = 5.5 feet. The area is 16 * 32 = 512 square feet. The volume is 512 * 5.5 * 7.48 = 21,063 gallons.
A round pool has a 21 foot diameter and an average depth of 4 feet. The area is pi * (21 / 2)^2 = 346.4 square feet. The volume is 346.4 * 4 * 7.48 = 10,364 gallons. If you fill it with a hose running at 9 gallons per minute, the fill time is 10,364 / 9 = 1,152 minutes, or about 19.2 hours.
FAQ
Why is the average depth used instead of the deep end? The deep end only describes part of the pool. Using the deep depth everywhere would overstate the volume. Averaging the shallow and deep depths gives a single figure that represents the whole pool, which is why pools that slope from one end to the other are calculated with (shallow + deep) / 2.
How accurate is the result for an irregular pool? The kidney and triangle formulas are approximations that fit common pool outlines closely, usually within a few percent. Real pools often have curves, steps, and benches that change the true volume. If you need an exact figure for chemical dosing, treat the calculated gallons as a close estimate and adjust from there.
How do I get the volume in liters or cubic meters? Set the volume unit to liters or cubic meters before you calculate. The math is done in cubic feet and gallons internally, then converted using 3.785 liters per gallon or 264.2 gallons per cubic meter, so the number you read already reflects the unit you chose.
