How this calculator works
Use the area of a rectangle or true ellipse and multiply by average water depth. The arithmetic mean of the two end depths assumes the bottom slopes linearly along a symmetric, constant plan outline. Steps, benches, curved slopes and separate diving wells change capacity and should be measured in sections. Water cost is volume times a per-cubic-metre rate, without fixed charges or tiered billing.
Formula
Rectangle area = length x width; ellipse area = pi x length x width / 4; average depth = (depth 1 + depth 2) / 2; V = area x average depth; cost = V x price per m3; depth 1 = 2V/area - depth 2.
Worked example
An 8 x 4 m rectangular pool with water depths of 1 m and 2 m averages 1.5 m deep and holds 48 m3. At $2/m3, filling costs $96. An elliptical pool with the same dimensions and depths holds 37.6991 m3.
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Frequently asked questions
Do I measure to the coping or water surface?
Measure actual waterline length and width and the filled water depths. Empty space above the waterline does not contribute to water volume.
Is every oval an ellipse?
No. A stadium shape with straight sides and semicircular ends has a different area. Use an outline-specific takeoff for that shape.
Can I infer one end depth from volume?
Yes, under the linear-bottom assumption. A negative inferred depth means the entered volume and known end depth are incompatible with that model.