Helpful information on common pond calculations for advance planning purposes



  • Determining the size liner to order
  • Calculating pond volume
  • Determining how many rocks you might carry
  • Determining the number of fish you can have
  • Determining the number of plants you will need.
  • Determining the pump you will need


Determining the size liner to order

First it is highly recommended that you perform your pond excavation prior to purchasing a liner.  In short -Just add 6 feet to the width and the length for ponds 2 feet deep. The depth of your water garden should vary, with three depths being ideal to accommodate both plants and fish. The shallow depth should be 6-10" for marginal plants, next a 12-18" depth for lilies, lotus, and submerged plants, and finally a 2’- 3’ depth for fish and over wintering your aquatic plants. The deeper water also helps to control water temperature throughout the year.

The length of liner = max length of pond + (2 times max depth) + minimum of 2' overlap.

The width of liner = max width of pond + (2 times max depth) + minimum of 2' overlap.

Example for an 8’ x 12’ pond 3’ feet deep:

Length requires 8’ + 6’ + 2’ = 16 foot Length

Width requires 12’ + 6’ + 2’ =  20 foot Width

To calculate the approximate gallons of water in your pond

It is important to know the total gallons of the pond to determine proper filtration, pump size, stocking capacity and dosages for water treatments and fish treatments. Measure the average length of your pond and multiply it by the average width and by the average depth and you will arrive with your total cubic feet of water. As there are *7.48 gallons per cubic foot, you can multiply your total cubic feet by 7.48 to get your total gallons in your pond. * 7.5 will be close enough.

For example, an 8 foot by 12 foot pond 2’ deep will be: 8 x 12 x 2 = 192 cubic feet.

Then multiply the 192 x  7.5 = 1440 gallons.

The formula for circular ponds is as follows: 3.14 x (1/2 diameter x 1/2 diameter) x depth = cubic feet; cubic feet x 7.48 = pond gallonage.

For example, an 8‘ Diameter  pond  2’ deep will be: 3.14 x 16 x 2  = 100.48 cubic feet.

Then multiply the 100.48 x 7.48 = 752 gallons.


To calculate the amount of rocks for a 2 foot deep pond

Boulders in a pond: length x width divided by 65 = tons of rock needed

Boulders in a stream: Ύ ton per 10 ft. length.

Boulders on the Waterfall: Ύ - 1 Ό tons of boulders for the waterfall face

Gravel in a pond: Ό - 3 inch gravel in a pond: tons of boulders used x .45

Gravel in a stream: Ό - 3 inch gravel in a stream: ½ ton per 10 ft. of length.


The number of Fish and Plants recommended in a pond

Fish: The general rule of thumb is 1" of fish per 10 gallons of water. This is only a very loose guideline, however as total surface area, flow rate, size and type of filtration are all to be considered when determining the right number of fish for your pond.

Plants: Phyto-filtration uses plants to filter pond water. Although plants are an excellent filtration aid, they are not the most stable or effective means for filtering. The main disadvantages include: lack of filtering in the spring and fall when the plants are dormant; expensive for the amount required; consume a large area; do not trap debris; are higher maintenance (trimming, separating, fertilizing and protecting in the winter); do very little to control the most toxic of pond chemicals - ammonia. Despite falling short as the pond’s main filter, plants are an excellent supplement to the filter and beautify the pond. Up to 75% of the pond’s surface should be covered with plants. This reduces evaporation, stabilizes the pond temperature, helps clear the pond water and provides a cool, shaded area for fish. Oxygenating plants have a clearing effect on the water but should NOT stocked heavier than a one gallon pot to 400 gallons of pond water or fish can be deprived of oxygen in the evening hours.

Calculating the amount of fish food to buy

Koi Fish can be fed  several times a day during warm weather months. Fish should be fed only what they will eat in a five-minute period. Fish food should be fresh and you should plan on buying only what you will need in a season. You should not feed at all when

the water temperature is 50 degrees or below. Colder temperatures slow down the digestive system of fish making it difficult or impossible to digest most fish foods.

Keeping  Spring/Fall between the two seasons will be fine if stored properly. Do not feed fish that has been laying around over a year.

Determining the size pump you will want

The total volume of water in the pond should pass through the filter every 1 to 2 hours. If the water circulates too fast, every 1/2 hour or less, the living beneficial bacteria on the filter media is washed away. If the water circulates too slowly, every 4 hours or less, the beneficial bacteria are deprived of oxygen and die off. The turn over rate must take into account head pressure, friction loss and pipe size.

Pump manufactures provide performance charts however, performance ratings suitable for your particular application should be carefully determined using several factors and not GPH alone. Review the electrical demands of the pump. Inexpensive pumps can cost 4 to 5 times more in electrical operating costs.  Centrifugal or non-submersible pumps offer variable speed and great flow rates for minimal energy usage.


Pump size is generally calculated based on gallons per hour output at 1 foot height, as the height increases the pump out put decreases.  An additional factor to consider is the length of hosing from the pump to the water feature. For every 10 feet of hosing resistance decreases pump output of one foot of lift.

Recommendations are general calculations intended to help you plan ahead.

We hope this information has been helpful.

Best Regards,