Pond Volume Calculator

Pick the shape of your pond and enter its size and average depth. You get the volume in gallons and liters, and the area of the water surface.

Units
Measure the water depth in several places and take the average. Do not use the deepest point: it gives too high a figure.
Pond volume898 US gal3,398 L
Water surface60 sq ft5.6 m²

A rectangular pond 10 ft (3.05 m) by 6 ft (1.83 m) with an average depth of 2 ft (0.61 m) holds about 898 US gal (3,398 L).

In UK gallons
747 UK gal
In cubic units
120 cu ft (3.4 m³)
Weight of the water
7,491 lb (3.4 tonnes)
  • Sloping sides and plant shelves hold less water than straight walls. That is why the average depth matters more than any other number here.
  • The most exact way: read your water meter before and after filling the pond.

What to work out next

Pond liner sizeThe liner to buy for this pondDosingTreatments for this much waterUnit converterGallons, liters, feet, meters

How to calculate pond volume

Every pond volume is the same sum: the area of the water surface, times the average depth.

Volume = surface area × average depth

In feet, the answer is in cubic feet: multiply by 7.48 for US gallons. In meters, the answer is in cubic meters: multiply by 1,000 for liters.

Pond shape Surface area
Rectangle or square length × width
Round 3.14 × half the distance across, squared
Oval 0.785 × length × width
Irregular 0.8 × length × width (an estimate)

Worked example. A rectangular pond is 8 ft long and 4 ft wide, with an average depth of 2 ft.

8 × 4 × 2 = 64 cubic feet. 64 × 7.48 = 479 US gallons (1,812 liters).

How to measure the average depth

Depth is where most pond sums go wrong. A pond with sloping sides and plant shelves holds much less water than the deepest point suggests.

  1. Measure the water depth, not the depth of the hole.
  2. Measure in several places: along the length and across the width, including the shallow shelves.
  3. Add the readings and divide by how many you took.

The more places you measure, the closer the answer. For a pond shaped like a round bowl with no flat bottom, the average depth is about half the deepest point.

Irregular ponds

A kidney-shaped or free-form pond has no exact formula. Measure the longest and widest points, as if the pond sat in a box, and take 80% of the box. That is the figure the pond maker Aquascape publishes, and it sits very close to the figure for an oval (78.5%).

It is an estimate. Other pond suppliers use figures between 75% and 85%, depending on how much the edge curves and how steep the sides are.

The exact way: use the water meter

If the pond is empty or you are about to fill it, read your water meter before and after. The difference is the true volume, shelves and slopes included. Write it down: you will need it every time you dose a treatment.

Why the volume matters

  • Treatments and salt are dosed by volume. Guess too high and you overdose the fish.
  • Pumps and filters are sized to move the whole pond in a set time.
  • Fish numbers depend on how much water there is.

Common mistakes

  • Using the deepest point instead of the average depth. It can double the answer.
  • Measuring the hole instead of the water. The water line is usually a few inches below the edge.
  • Treating an oval or kidney pond as a rectangle. That overstates the volume by about a fifth.
  • Mixing units, such as feet for length and inches for depth. Use one unit for all three.
  • Mixing up US and UK gallons. A UK gallon is a fifth bigger.

Questions and answers

How do I calculate how many gallons my pond holds?

Multiply length × width × average depth in feet, then multiply by 7.48. A pond 8 ft by 4 ft with an average depth of 2 ft holds 8 × 4 × 2 × 7.48 = 479 US gallons.

How do I work out pond volume in liters?

Multiply length × width × average depth in meters, then multiply by 1,000. A pond 3 m by 2 m with an average depth of 0.6 m holds 3 × 2 × 0.6 × 1,000 = 3,600 liters.

How do I calculate the volume of a round pond?

Multiply 3.14 by half the distance across, squared, then by the average depth. A round pond 3 m across and 1 m deep holds 3.14 × 1.5 × 1.5 × 1 = 7.07 cubic meters, which is 7,070 liters.

How do I measure an irregular pond?

Measure the longest and widest points and the average depth, work out the volume as if it were a rectangle, then take 80% of it. It is an estimate; filling through a water meter gives the exact figure.

How many gallons are in a cubic foot of water?

7.48 US gallons, or 6.23 UK gallons. One cubic meter is 1,000 liters.

Numbers for standard tanks

Have a standard tank? Its size, weight, heater and stocking are already worked out.

Sources

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