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 pipe | Optial 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 |
| 350 | 70 | 2,000 | 12-18 |
| 700 | 140 | 4,000 | 24-36 |
| 1,400 | 250 | 7,500 | 42-62 |
| 2,800 | 400 | 10,000 | 65-100 |
| 5,600 | 800 | 24,000 | 130-200 |
| 11,200 | 1,600 | 40,000 | 260-400 |
Pond and Stream Plant Selections
| Pond size | Marginal plants | Waterlilies | Floaters | Submerged plants | Lotus |
| 6'x8' | 6 | 1 | 3 | 8 | - |
| 8'x11' | 9 | 1 | 5 | 15 | - |
| 11'x16' | 12 | 2 | 7 | 29 | - |
| 16'x21' | 15 | 3 | 15 | 91 | 1 |
| 21'x26' | 21 | 5 | 25 | 91 | 1-2 |
| Stream per 10' | 3-6 | - | - | - | - |