Round Pool Water Volume Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/8/2026
A round pool's water volume is calculated with π × (diameter ÷ 2)² × average depth. A pool 4.5 m in diameter with an average depth of 1.2 m holds about 19.1 m³, or about 19,085 liters.
Explanation
Unlike a rectangular pool, whose volume is simply calculated by length × width × depth (see our rectangular pool volume calculator), a round or circular above-ground pool requires first calculating the area of a circle (π × radius², the radius being half the diameter) before multiplying it by the depth to get the volume. This difference in shape also explains why, for the same diameter and side length, a round pool always holds a bit less water than a square pool of the same width: a circle inscribed in a square occupies about 78.5% of its surface. For a pool with a sloped bottom (deeper in the center or on one side), the average depth between the shallowest and deepest points gives an estimate accurate enough for this purpose, exactly as for a rectangular pool. Knowing this volume is notably useful for dosing water treatment products in proportion to the pool's total volume: see our pool shock chlorine dosage calculator for the next step once the volume is known.
Example: a round pool 4.5 m in diameter, average depth 1.2 m
Inputs
Diameter: 4.5 m. Average depth: 1.2 m.
Calculation
Radius = 4.5 ÷ 2 = 2.25 m. Area = π × 2.25² ≈ 15.90 m². Volume = 15.90 × 1.2 ≈ 19.09 m³, or about 19,085 liters.
Result
This round pool needs about 19,085 liters to fill completely.
Frequently asked questions
Does this calculator work for an oval pool?
No, it is specifically designed for a perfectly circular pool. An oval pool uses the formula for the area of an ellipse (π × semi-major axis × semi-minor axis) rather than that of a circle, a slightly different calculation not covered here.
Why does a round pool hold less water than a square pool of the same width?
Because a circle inscribed in a square only occupies about 78.5% of that square's surface (the ratio between the circle's area and the square's area is exactly π ÷ 4). For the same diameter as the square's side, the round pool therefore mechanically holds about 21.5% less water.
How do I measure the diameter of an already-installed above-ground pool?
Measure the greatest possible distance from one inner edge to the other, passing through the center of the pool. For a self-supporting or tube-frame pool, the diameter is generally stated directly on the packaging or the manufacturer's manual.