If measuring in feet
length x width x depth x 6.24 = gallons
If measuring in metre’s
length x width x depth x 1000= litres then x 0.22 =gallons
if your pond is circular measure in metres then
half the diameter x by itself x 3.14 x depth x 1000 x 0.22 = gallons
when measuring try to take an average for example if a pond is 5ft wide for half its length and 7ft wide for the other half we would take the average width at 6ft! The same applies to the water depth.
If you are working out how many gallons your pond holds for a filtration system it is ok to over estimate on water volume but if you need pond gallons to treat sick fish then try to be within 10% so you do not overdose your stock!
We recommend using a pond flow meter when first filling a pond, this counts how many litres your pond holds exactly when it is full !