Maintaining a swimming pool is more than just skimming leaves and checking the chlorine. To effectively treat your water with chemicals, size a new heater, or even estimate your water bill, you must know exactly how many gallons your pool holds. Guessing can lead to chemical imbalances that are either unsafe or expensive to fix.
Pool Volume Calculator
The Fundamental Formula
The basic logic for calculating pool volume involves finding the surface area of the water and multiplying it by the average depth. Once you have the cubic footage, you multiply by a conversion factor to get the total gallons.
- 1 Cubic Foot of Water = 7.48 Gallons
- Average Depth = (Shallow End Depth + Deep End Depth) / 2
Step-by-Step Calculation by Shape
1. Rectangular or Square Pools
Rectangular pools are the simplest to calculate. You simply multiply the length by the width to get the square footage, then multiply by the average depth.
Formula: Length x Width x Average Depth x 7.48 = Total Gallons
Example: A 30ft x 15ft pool with a shallow end of 3ft and a deep end of 9ft. Average depth is 6ft. (30 x 15 x 6 x 7.48) = 20,196 gallons.
2. Circular / Round Pools
For round pools (mostly above-ground models), you need to find the radius (half the diameter). The formula uses Pi (π) which is approximately 3.14.
Formula: 3.14 x Radius² x Average Depth x 7.48 = Total Gallons
Example: A 24ft round pool (12ft radius) with a constant 4ft depth. (3.14 x 144 x 4 x 7.48) = 13,524 gallons.
3. Oval Pools
Oval pools are slightly more complex because they combine rectangular and circular geometry. A common shortcut used by pool professionals is to use a multiplier of 5.9 instead of 7.48 when calculating based on the long and short axes.
Formula: Long Axis x Short Axis x Average Depth x 5.9 = Total Gallons
Why Average Depth Matters
Most residential pools have a "slope" or a "hopper." If your pool is a constant 4 feet deep, your average depth is simply 4. However, if you have a shallow end of 3 feet and a deep end of 8 feet, your average depth is 5.5 feet. If the deep end is a small "well" rather than a consistent slope, your calculation may be slightly over-estimated, but it remains the industry standard for chemical dosing.
Irregular Shapes (Kidney or Freeform)
For kidney-shaped or freeform pools, the most accurate method is to treat the pool as two circles or rectangles joined together. Alternatively, calculate the average width by measuring the widest and narrowest parts, adding them, and dividing by two. Then use the rectangular formula with this "average width."
Pro Tip: Meter Readings
If you are filling your pool for the first time or after a complete drain, the most accurate way to know the volume is to check your water meter before you start and after you finish. Subtract the initial reading from the final reading to get the exact amount of water used.