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How To Calculate Water Volumes For Any Garden Fish Pond of Any Shape

If your pond is not a simple rectangle or square the calculation is more difficult. If you are not totally accurate do not be too concerned because we are looking for an approximate volume. However you should aim to be within 10% to 15% accuracy.

In making approximations the simplest way to do this is to assume the pond is surrounded by a rectangle and then ask yourself what proportion of the rectangle is covered by water. See the sketch below to assist in understanding this measurement technique.

Lets say the proportion is 50% and the depth is once more constant at 0.5 metres and the rectangle around the pond is 3 metres long x 2.8 metres wide. The volume is calculated as follows:

3.0 x 2.8 x 0.5 x 50/100 = 2,1 cu.metres = 2.1 x 1,000 = 2,100 litres

If the depth is not uniform then use the average depth to calculate the volume.

Another more accurate approximation can be made by counting the small squares into which the pond has been divided as in the diagram above. This is the method explained in detail:

  1. The pond was first drawn to scale using graph paper or something similar like a spreadsheet (this sketch was done on a spreadsheet):

  2. Each square in the sketch has a constant size. As you can see the total squares covered in the total rectangular area is 11 x 12 = 132 squares.

  3. The total yellow squares must now be estimated. We estimate about 21 full squares are covered by the yellow bits. If you get a bit different it does not matter much.

  4. Now count the white squares we get 56.

  5. This means you can now calculate the number of squares covered by the blue pond as follows:

  6. = 53 squares

  7. If each square is 0.2 x 0.2 metres then area covered by pond is as follows:

  8. 53 x 0.2 x 0.2 = 2.12 sq metres

  9. If average depth of pond is 0.5 metres then pond volume is

  10. 2.12 x 0.5 x 1,000 = 1,060 litres

Knowing the volume of your pond is important if you want to specify other equipment correctly. Once again if you are not sure seek help.

While considering pond volume 1,000 litres of water is a good volume to hold about 1 kg of fish.

Here is that conversion table again.

Pond volume conversion factors

this page reprinted with permission of The Pond Professor


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This table will help you with converting units from one type to another (for example 1 Imperial Gallon/min = 0.16 Cu. Feet/min, 4.55 Litres/min or 0.005 Cu. Metres/min) ...

Unit Imp Galls/min Cu Feet/min Litres/min Cu. M/min
Imp. Gallons 1 0.16 4.55 0.005
Cu. Feet 6.23 1 28.32 0.028
Litres 0.22 0.04 1 0.001
Cu. Metres 220 35.32 1,000 1

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