Stone: Quantity of Rock & Gravel for an 18-36" / 45-90 cm Deep Pond
Updated
Boulder calculation for a 750 sq. ft. / 70 sq meter or smaller pond:
Formula: (Length of Pond x Width of Pond) / 40 = Tons of Boulders
Use boulders in a 1:2:1 ratio:
6-12” / 15-30 cm
12-18” / 30-45 cm
18-24” / 45-60 cm
Depth Adjustment Factors:
18" / 45 cm depth:
Multiply the calculated tonnage by 0.85
24" / 60 cm depth:
The calculated tonnage is the correct number of tons
30" / 75 cm depth:
Multiply the calculated tonnage by 1.2
36" / 90 cm depth:
Multiply the calculated tonnage by 1.5
Example for Metric Conversion:
1 Ton (US) = 2,000 lbs = 907.18 kg
Adjust calculations based on the depth factor and ratio guidelines.
Gravel calculation for the above pond:
Total Tons of Boulders in the Pond at 24" (60 cm) Deep X 30% = Tons of Gravel Needed for the Pond
To calculate the required amount of gravel, multiply the total weight of the boulders used in the pond by 30%.
Total Gravel Amount Depends on Building Style
If you prefer to backfill all gaps behind the wall boulders with gravel, you will need to increase the quantity of gravel required.
If backfilling the gaps behind the boulders, multiply the total boulders by 40-45%
Recommended Gravel Sizes
Ideally, half of the amount of River Gravel would be:
3/4" (20 mm) size.
The other half would be 1–3" (40–70 mm) size.
Adjust the sizes based on what is available from your rock supplier.
If you are making the pond 18" or 36" deep instead of the standard 24" depth, then you would still use the formula for a 24" deep pond to determine the total gravel needed for the pond. The gravel amount will not change based on the depth for standard sized ponds.