Hi Kumunryo,
A while since I've done this so here goes:
Square And Rectangle Ponds
Length x Width x Average Depth (in feet or meters) = Volume of Pond
Example:
9.8’ (3.0m) L x 9.8’ (3.0m) W x 4.9’ (1.5m) D = A pond volume of 571 cubic feet(13.5 cubic meters).
=13,500 litres or 2973.5 imperial gallons
Round Ponds
πr ² x depth (3.142 x Half diameter squared x Depth)
Example:
πr² x depth
3.142 x (1.5m x 1.5m) x 1.5m = 10.6 cubic meters.
10,600 litres or 2334 imperial gallons
I've sanity checked the figures on this.
http://www.watergardeningdirect.com/Adv ... ulator.htm
Martin