How to Build a Pond
Pond Installation
The most common materials with which to build your pond are flexible pond liners or solid preformed ponds. Whichever you select, we recommend you always follow the manufacturer’s instructions for installation. However, this guide provides a brief description for installing a preformed pond or flexible pond liner.
Remember, ponds should be placed in a sunny location (with a minimum of six hours of sunlight a day) and away from trees and bushes, if possible. You may want to place the pond within easy view from your most used outdoor space. Your pond should be accessible to a garden hose and electrical line. Consult your electrician for proper electrical requirements.
Calculating the Volume of Your Pond
It is important to know the volume of water in your pond. Knowing the volume of water can help you determine the number of fish the pond can hold. Knowing the volume is most important when calculating partial water changes and using pond maintenance and feeding products. The easiest method to calculate the volume of your pond is to measure the amount of water used to initially fill your pond. Before you fill your pond, for the first time, note the time in seconds it takes to fill a five U.S. gallon (20 L) bucket with tap water at a constant flow rate from a garden hose. Then, fill the pond at this same constant flow rate, using the garden hose. Record the time (in seconds) that it takes to fill the pond. Then use the following formula to determine the volume of your pond.
Volume of pond (in gallons or liters) 
Time required to fill pond (seconds) 
x  Volume of bucket (Gal/L) 

=  
Time required to fill bucket (seconds) 
If the pond is already filled, the volume can be calculated using one of the following formulas. Then, convert volume to gallons or liters.
Square And Rectangle Ponds
Length x Width x Average Depth (in feet or meters) = Volume of Pond
Example:
9’ (2.74m)L x 6’ (1.83m)W x 2’ (.6m)D =  A pond volume of 108 cubic feet (3 cubic meters) 
Round Ponds
Top Diameter x Bottom Diameter x Height (in feet or meters) x 7.85 = Volume of Pond
Example:
(3’ (.9144m)TD x 3’ (.9144m)BD x 2’ (.6m)H) x .785 =  A pond volume of 14.13 cubic feet (.39 cubic meters) 
Converting Volume to Gallons/Liters
Cubic feet (ft3) x 7.48 = Gallons
Cubic Meters (m3) x 1000 = Liters
Multiply 108 ft3 x 7.48 = 807 Gallons or 3 m3 x 1000 = 300 Liters
Note : 1 UK Imperial Gallon = 1.2 US Gallons or 4.5 liters. Use the above formulas to figure US gallons. Then divide that answer by 1.2, which will give you the UK Imperial Gallons. ( __US Gallons / 1.2 = __ UK Gallons)