Koi

Keith Holmes says...

To work out the gallonage of a square or rectangular pond:

In feet and inches: length x width x depth x 6.25 = gallons

For example, a pond that is 10ft long by 8ft wide by 5ft deep would have: 10 x 8 x 5 x 6.25 = 2,500 gallons 

In metres: length x width x depth = m³ (1m³ = 220 gallons or 1,000l)

For example, a pond that is 2.5m long by 2.5m wide x 1.5m deep = 9.38m³; 9.38 x 220 = 2,064 gallons 

To work out the gallonage of a circular pond:

 In feet and inches: π (3.14) x radius (half the diameter) squared x depth x 6.25 = gallons

 For example, a pond with a diameter of 10ft will have a radius of 5ft; if the pond is 5ft deep, the gallonage is: 3.14 x 5m² x 5 = 392.50. 392.50 x 6.25 =
2,453 gallons 

In metres: π (3.14) x radius squared x

depth = m³

For example, a pond with a diameter of 3m would have a radius of 1.5m; if the pond is 1.5m deep the gallonage would be: 3.14 x 1.5m² x 1.5m = 10.6m³. 10.6 x 220 = 2,332 gallons

If you want to work out these figures in litres, one gallon is equal to 4.54609l.
If your pond is an unusual shape or has varying levels of depth, draw it onto graph paper, and then divide it up into zones that have equal depth or are of a more uniform shape. Having done this, apply the formulas shown to work out the gallonage of each zone, then add them all together to give you the total gallonage.