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Helpful Formulas and Calculations

Below appear a series of formulas that can be used to spec out materials for your water garden. These formulas have been derived from our professional experience and are intended to provide very rough suggestions. Every pond project is completely unique, so you might find you will need more or less materials than what these formulas suggest.

Rocks and Gravel Approximations

Quantity of boulders for a pond:

     Length x Width (in feet) / 40 = Tons of boulders
     For every 1 ton of 6-12" boulders, use 2 tons 12-18" boulders and 1 ton of 18-24" boulders.

Quantity of boulders for a stream:

     1 1/2 tons for every 10' of stream using a 1:2:1 ratio as above

Quantity of gravel in a pond:

     Pond gravel = 25% of total tons of boulders used in pond

Quantity of gravel in stream:

     Stream Gravel = 25% of total tons of boulders used in stream

Quantity of boulders for face of waterfall box:

     22" - 1 ton of mixed boulders
     30" - 1 1/2 tons of mixed boulders
     40" 3 tons of mixed boulders

Quantity of Boulders for retaining wall:

     1 ton of 12-18" boulders will cover 10 linear feet
     1 ton of 18-24" boulders will cover 5 linear feet

Quantity of stone used in a bog filter (per 10 sq ft of bog):

     900 lbs 1 1/2-2" Washed River Gravel
     900 lbs 1/2-1" Washed River Gravel

Quantity of boulders used around the perimeter of a bog filter

     1/2 ton of 6-12" boulders will cover 20 linear feet
     1/2 ton of 12-18" boulders will cover 10 linear feet

Volume Approximations

See also our Calculating Water Volume in Ponds article for more a more in-depth discussion of methods to calculate volume of a pond.

Approximate gallons of water in a pond

      Length (ft) x Width (ft) x 0.80 x Average Depth (ft) x 7.48 = Total Gallons in Pond

Approximate gallons of water in a stream

      Length (ft) x Width (ft) x 0.25 x Depth (ft) x 7.48 = Total Gallons in Stream
      (Length = measurement down the middle of the stream plus the rise)

Approximate gallons required in a pond-less basin

      Total Gallons in Stream x 2.5 = Total Gallons Required in Basin

Approximate gallons of water in a pond-less basin

      With stone/gravel: Length (ft) x Width (ft) x Depth (ft) x 2.2 = Gallons in Basin
      With Large Matrix: Number of Matrix x 32 = Gallons in Basin
      With Small Matrix: Number of Matrix x 17 = Gallons in Basin

Basin Matrix capacities

      Large Matrix (4.3 cu. ft.) holds 32 gallons
      Small Matrix (2.3 cu. ft.) holds 17 gallons

Suggested stream flow rates

      Sheet falls: 1,500 gph per foot width
      Bouldering falls: 3,000 gph per foot width

Other Helpful Data

Pipe and Tubing Flow Chart

Inside diameter of pipeOptial flow rate (gph)
1/2"350
3/4"750
1"1,200
1 1/2"2,900
2"4,600
two- 2"9,200
3"12,000
4"18,500

Bog Filter Sizing Chart

Note: These are basic guidlines and can change based on site conditions.

Surface area of pond (sq. ft.)Bog size (sq. ft.)Flow rate (gph)Plants
350702,00012-18
7001404,00024-36
1,4002507,50042-62
2,80040010,00065-100
5,60080024,000130-200
11,2001,60040,000260-400

Pond and Stream Plant Selections

Pond sizeMarginal plantsWaterliliesFloatersSubmerged plantsLotus
6'x8'6138-
8'x11'91515-
11'x16'122729-
16'x21'15315911
21'x26'21525911-2
Stream per 10'3-6----