Pool Volume Calculator: Gallons, Water Depth and Checked Examples

Estimate rectangular, circular and elliptical pool volumes in US gallons. Checked examples and tables, actual water-depth assumptions and limits of the estimate.

A rectangular pool measuring 16 × 32 feet with an average water depth of 5 feet holds about 19,150 US gallons. The Pool Volume Calculator estimates water volume for rectangular, circular and elliptical footprints. It reports US gallons, liters and cubic feet.

Use actual internal water dimensions. Wall height, advertised pool size and water depth are different measurements. Volume is useful for maintenance planning, but a geometric estimate does not determine a chemical dose or establish that water is safe for swimming.

Three Pool-Volume Formulas#

The calculator uses these idealized shapes, with dimensions in feet:

An oval mode using an ellipse does not exactly represent every curved pool. A straight-sided pool with rounded ends, a kidney-shaped pool and a true ellipse have different areas. For complex designs, use the builder's water-volume specification or calculate suitable sections separately.

For US liquid gallons, multiply cubic feet by 7.48052. The exact ratio is 1,728 cubic inches per cubic foot divided by 231 cubic inches per US gallon; 7.48052 is its rounded value. The calculator converts gallons to liters using 3.78541.

Rounding the gallon factor to 7.5 overstates the result by about 0.26%, or approximately 52 gallons per 20,000 gallons. Measurement and shape uncertainty can be larger than this rounding difference.

Measure Water Depth and Account for the Bottom Shape#

For a flat bottom, enter the same actual water depth in both depth fields. For a single linear slope across a rectangular pool, the average is:

Average depth = (shallow water depth + deep water depth) ÷ 2

For example, depths of 3 and 7 feet give a 5-foot average. On a linear slope, that also equals the depth halfway along the slope. This shortcut does not describe every pool bottom.

If a pool has a long shallow shelf, a separate slope, a deep well, steps or benches, divide it into sections and sum their volumes. Averaging only the shallowest and deepest measurements ignores how much area each depth occupies.

Consider a 32-foot-long rectangular pool with a 16-foot-wide footprint. If its first 24 feet are flat at 3 feet deep and its last 8 feet slope linearly from 3 to 7 feet, then:

Shallow section = 24 × 16 × 3 = 1,152 cubic feet
Sloped section  = 8 × 16 × ((3 + 7) ÷ 2) = 640 cubic feet
Total           = 1,792 cubic feet
Gallons         = 1,792 × 7.48052 ≈ 13,405

Using a 5-foot average across the entire footprint instead would give 19,150 gallons. The difference comes from the bottom geometry, not from rounding. This example excludes steps, benches and other displaced volume.

Reproduce Three Worked Examples#

Rectangle: A 16 × 32-foot pool with a 5-foot average depth:

16 × 32 × 5 = 2,560 cubic feet
2,560 × 7.48052 = 19,150.1312 US gallons
Displayed volume: 19,150 gallons

Circle: An 18-foot diameter pool with a constant 4-foot water depth:

Radius = 18 ÷ 2 = 9 feet
π × 9² × 4 = 1,017.8760198 cubic feet
Volume ≈ 7,614.2419 US gallons
Displayed volume: 7,614 gallons

Ellipse: A 20 × 12-foot elliptical pool with a constant 4-foot water depth:

π × (20 ÷ 2) × (12 ÷ 2) × 4 = 753.9822369 cubic feet
Volume ≈ 5,640.1792 US gallons
Displayed volume: 5,640 gallons

The calculations retain precision until display. The rounded cubic-foot figures in the explanations should not be used as intermediate inputs when reproducing the final decimals.

Rectangular Pool Reference Table#

These are ideal rectangular volumes, rounded to whole US gallons. The depth headings mean average water depth, not wall height.

Circular Pool Reference Table#

These rows assume a circular footprint and constant water depth. Measure the water surface to the bottom; do not substitute the full pool-wall height or deliberately overstate the volume.

For a deck around a circular pool, calculate the outer deck footprint and pool footprint separately, then subtract the pool area yourself. The Square Footage Calculator provides individual rectangle, circle, triangle and L-shape modes; it does not perform an automatic composite subtraction.

Use Volume Alongside Product Instructions#

CDC's home-pool guidance emphasizes checking water chemistry and following manufacturer directions. CDC's chemical-safety guidance also directs users to product labels and safety instructions.

A product's directions depend on that product and the measured water conditions. Do not assume every label uses the same reference volume or treatment amount. This article supplies volume estimates, not chemical dosages. Inflating the water-depth input is not a safety margin.

For saltwater equipment, use its specified target and a measured current salt concentration. The Pool Salt Calculator provides a separate estimate; the equipment instructions still determine suitable operating conditions.

Volume Does Not Fully Specify Pumps or Filters#

Volume divided by an assumed circulation time gives a theoretical flow rate. For example, 20,000 gallons divided by a hypothetical 8-hour period is 2,500 gallons per hour, or about 41.7 gallons per minute. This arithmetic is not a universal equipment recommendation or a guarantee that every part of the pool circulates uniformly.

Use the pump and filter manufacturers' specifications, plumbing conditions and applicable requirements when choosing equipment. A sand filter's media type and quantity should come from its model-specific instructions. Our Sand Calculator estimates rectangular material volumes from length, width and depth; it does not model cylindrical filter tanks or specify replacement filter media.