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Lagoon Pool Volume Calculator

Lagoon pools curve like a natural pond, so no single formula is exact. The 0.785 area factor used here gets most lagoon builds within a few percent of their true volume.

Lagoon pool with the measurements needed for a volume calculation

Calculate your lagoon pool volume

1. Pick your pool shape

An organic, curved shape designed to look like a natural lagoon.

2. Enter your measurements

Measure in feet or meters. You always get gallons and litres back.

3. Set your depth

Average depth = (shallow + deep) / 2.

Your pool volume result

Pool volume

17,440 gallons

66,019 litres

Cubic feet
2,331 cu ft
Cubic metres
66.0 m3
Surface area
424 sq ft
Average depth
5.50 ft
Pool shape
Lagoon
How we calculated this

Shape: Lagoon. Dimensions used: Maximum length 30 ft, Maximum width 18 ft. Depth: 3 ft shallow and 8 ft deep, averaged to 5.50 ft. Formula: Volume = length x width x 0.785 x average depth. Conversion: cubic feet x 7.48 = US gallons, gallons x 3.785 = litres, cubic feet x 0.0283 = cubic metres.

This shape uses an average area factor, so treat the number as a close estimate rather than an exact volume.

How the lagoon pool volume calculator works

Multiply the maximum length by the maximum width, then by 0.785 to account for the curving edges. Multiply the result by average water depth.

The factor comes from the ratio between a circle and the square that contains it, which is close to how a lagoon sits inside its bounding rectangle.

The formula

Volume = length x width x 0.785 x average depth

Measure: Maximum length, maximum width, average depth.

Worked example

A lagoon measuring 30 feet long and 18 feet wide gives 30 x 18 x 0.785, or 423.9 square feet.

At an average depth of 4.5 feet that is 1,908 cubic feet, close to 14,270 gallons or 54,010 litres.

Tips before you measure

Measure the longest and widest points of the water, even if they are not at right angles to each other.

Beach entries hold very little water. Leave that sloped area out of the width measurement or the result runs high.

Lagoon pool volume FAQs

How accurate is a lagoon estimate?

Usually within 5 to 10 percent. Deep curves and beach entries widen the margin, so round up for chemical doses.

Should I include the beach entry?

No. Water there is only inches deep, so counting it at average depth overstates the volume.

Is lagoon the same as freeform?

The maths is the same. Lagoon usually describes a softer, more rounded outline built to look natural.

Other pool shapes

Not quite the right outline? The main pool volume calculator covers all 20 shapes with the same units and formulas.