Various Water Garden Measurements
Part 1
by Wayne Smith

Ontario Water Garden Society Newsletters
Vol. 3 Issue 1 Feb. 2001

Web site

The purpose of this article is to help you in calculating various requirements around your water garden. I have used information from my own experience, plus various articles and forums on web sites. If you are just starting out as a 'ponder' these calculations should help you get it right the first time. If you have an existing pond and are having problems, following these calculations may explain some of them. If you are thinking of changing your pond, these calculations will help guide you and lastly, if you are wondering if it's safe to add more fish, the answer is in the calculations below.

Determining size of liner required

For the length of liner required calculate Max. length of pond + (2 x max. depth of pond) + 2 feet overlap at each end

For the width of liner required calculate Max. width of pond + (2 x max. depth of pond) + 2 feet overlap on each side

Be sure to measure across the maximum length and width and at right angles to each other.

As an example, if you have decided on a location that measures 10 ft. by 13 ft. and you want 2 ft. deep and including a minimum liner overlap of 2 feet for both length and width, you determine a required liner size of 18' x 21'. (10 +(2+2) +(2 +2)) by (13 + (2+2) +) 2 +2))

Note - you may be able to use shorter overlaps. The overlap needs to be large enough so that it can go under the edging materials and then rise up a couple of inches at the back of the material to prevent overflow

When planning a new pond you may want to consider that liners often are sold at fixed sizes or at least in widths at 5' multiples. So in the example above you would be buying either 18' x 20' which would reduce the pond length by 1 foot or buy 18' by 25' which would allow a combination of greater length or depth in part or all of the pond.

Some common conversions

To calculate power consumption:

Volts x Amps = Watts

To calculate yearly cost of operation: Watts divided by 1000 x the price of electricity in $ per kilowatt hour x 24 hours x number of days in use in a year

One U.S gallon = approx. 0.834 Imperial gallons

One U.S. gallon = approx. 3.78 liters

One Imperial gallon = approx. 1.2 U.S. gallon

Caution - most but not all items such as filter and pumps sold in Canada use US gallons but not all. Not understanding which measurement is meant in something you read can lead to improper sizing of equipment and incorrect dosing of medicine. If a product gives a liter value and a gallon value without indicating US or imperial gallons, you can use the ratio above to determine which it is.

To help with some dosage rates for medicine:

PPM (parts per million) = mg/liter or milligrams per liter
1000 milligrams = one gram
1000 milliliters = 1 liter
or one liter holds 1000 milliliters, abbreviated 1000 ml
ppt (parts per thousand) = ten times weight percent, since percent is simply parts per hundred
Each USA gallon holds 8.4 pounds of water, each imperial or UK gallon holds 10.0 pounds per gallon.
Each pound hold 454 grams.
A ml of water weighs very close to one gram and occupies a volume of one cubic centimeter or cc.


Potassium permanganate is a powder used by some Koi keepers to control parasites. It is recommended to use at 4 PPM. First create a stock solution that can be used for multiple treatments. Measure a level teaspoon of PP powder (approx. 7 grams) and put in a container, which will hold a liter of water. Add a liter of water and mix until the powder is dissolved. You now have a stock solution, which has 0.007 grams per milliliter. If you are doing the treatment in a quarantine tank which holds 67 US gallons the calculation is - 67 times 8.4 pounds per gallon = 563 pounds of water. 563 times 454 grams per pound gives 255,000 grams of water, or 0.255 million grams of water. 0.255 million grams times 4 parts per million of PP gives 0.255 times 4 = 1.02 grams of PP needed. 1.02 grams of PP needed divided by 0.007 grams PP per ml = 146 ml of the stock solution described above to obtain a 4 PPM charge of PP to the 67-gallon tank.

You will find some articles, which give dosage rates in metric and quote rates per ton of water. One ton of water equals one cubic metre of water, which contains 1,000 liters and weighs 1,000 kilos. To calculate the tonnage of a system from imperial gallons divide the total pond volume by 220. For example if a pond contains 7,500 imperial gallons it holds 34.09 tons (7,500 divide by 220). To calculate the tonnage of a system from US Gallons divide the total pond volume by 264. For example if a pond contains 10,000 US Gallons it holds 37.87 tons (10,000 divide by 264).

To calculate the square foot surface area of a pond:
For a rectangular pond - multiply average length by average width
For a circular pond - multiple half the diameter by half the diameter by 3.14

Actual Pond Volume

Average length (ft) x average width (ft) x average depth (ft) = total cubic feet x 7.48 = Actual Pond Volume (US gallons)

For Actual Pond Volume in Imperial gallons multiply total cubic feet by 6.25


Pond is 12' avg. length x 10' avg. width x 2' avg. depth

U.S. Pond Volume: 12 x 10 x 2 = 240 cubic feet. C.f. x 7.48 = 1,795 gallons
Imperial Pond Volume: 12 x 10 x 2 = 240 cubic feet. C.f. x 6.25 = 1,500 gallons

 Note - Unless your pond is box shape, you will not be using the same numbers used in calculating liner sizes. To calculate a good average, measurements should be taken at several points.

If starting with an empty pond options include using a flow meter, monitoring water tank measurement change or timing how long it takes in seconds to fill a bucket such as 10 gallon and then time how long it takes to fill the pond. If it takes 15 seconds to fill 10 gallons and it takes 3000 seconds to fill the pond then you have 2000-gallon pond. In determining the total water to be filtered, additions must be made for volume in the tubing, filters and any other areas such as a header pond for the waterfall.

Effective Pond Volume

When selecting the proper size equipment for your pond, actual volume alone is not enough. You must determine the effective volume of your pond, which is influenced by various environmental factors. Determine if your pond is affected by direct exposure to sunlight, shallow depth, or climate conditions, and add to the actual volume by the factors listed below:

If average pond water depth is less than 2' 6": add 25 % (This is a guide and is not meant that if your pond is 2' 5" add 25% and if 2' 7" then add 0% - shallow water heats up more and therefore requires more filtration so if around 2' 6" use a reasonable value).

Pond is located in full sunshine (6 plus hours): + 25 %
Pond is located in part sunshine (4 - 6 hours): + 15 %

Pond is located in Northern climate: + 0 % (if this will be used by someone in southern climate zones the factor would be + 35% for Florida and a descending amount as you go north towards 0% in Ontario. The zone ranges are 1-5 add 0%--6-7 add 15%--8-10 add 35%

Example 1

If you have a 2,500-gallon pond, 4' deep, located in full sunshine and you live in Ontario, the effective volume of your pond is 3,125 gallons (2,500 + 25 %).

Example 2

If you have a 1,500 gallon pond, 2' deep and exposed to part sunshine in Kentucky, your pump and/or pond filtration equipment would need to be increased by 55 % (25 + 15 + 15). You would therefore base your selection on a pond volume of 2,475 gallons.

Note - your filtration system needs to circulate the total effective pond volume every 1 to 2 hours


Go to Part 2