Formulas behind the pool calculator
The OmniCalculator pool page uses geometry plus average depth. That means you first calculate the pool's plan area, then multiply it by the average water depth.
Rectangular pool: V = l × w × (d1 + d2) / 2
Oval or circular pool: V = (π × l × w / 4) × (d1 + d2) / 2
For a circular pool, length and width are both the diameter, so the oval formula naturally reduces to the area of a circle times average depth.
Average depth matters
If the floor slopes from a shallow end to a deep end, the average depth is the midpoint between those two measurements. This is the key step behind the familiar question, "How many gallons is my pool?"
Why pool volume matters
Once you know the pool volume, you can estimate fill-water cost, chemical dosing, heating demand, and total water weight. Those downstream quantities are often more useful in practice than the raw geometry alone.