Drainage Gravel Calculator
Estimate the volume in cubic yards, cubic feet, and total weight in tons of drainage gravel required to backfill French drains, leach fields, or trenches.
Calculation Results
Total volume of drainage gravel needed in cubic feet, including waste.
Total volume of drainage gravel needed in cubic yards, including waste.
Total weight of drainage gravel needed in tons.
How This Calculator Works
To use the Drainage Gravel Calculator:
- Enter the running length of the drainage trench.
- Enter the width of the trench (standard French drains are typically 12 to 18 inches wide).
- Enter the depth of the trench (typically 1.5 to 3 feet deep).
- Specify the material density (1.4 tons/cu yd is standard for clean aggregate).
- Add a waste allowance. 10% is recommended because stone settling will occur.
Formula & Calculations
Drainage trench gravel volume is calculated by multiplying length, width, and depth, and adding a waste factor (typically 10% to cover loose settling):
Volume (Cubic Feet) = Length × Width × Depth × (1 + Waste / 100)
To convert from cubic feet to cubic yards, we divide by 27:
Volume (Cubic Yards) = Volume (Cubic Feet) / 27
Weight is calculated by multiplying the cubic yard volume by the density of the drainage gravel (expressed in tons per cubic yard):
Weight (Tons) = Volume (Cubic Yards) × Density
For standard drainage stone (such as clean 3/4-inch aggregate), the density is approximately 1.4 tons per cubic yard.
Step-by-Step Calculation Examples
French Drain Trench
A French drain trench measuring 50ft long by 1.5ft wide by 2ft deep, filled with clean 3/4-inch drainage stone, assuming standard density (1.4 tons/cu yd) and 10% waste.
- length: 50
- width: 1.5
- depth: 2
- density: 1.4
- waste: 10
- volume_cu_ft: 165.0 cu ft
- volume_cu_yd: 6.11 cu yd
- tons_needed: 8.56 tons
Frequently Asked Questions
What type of gravel is best for drainage trenches?
Clean, washed crushed stone or gravel that is 1/2 inch to 1.5 inches in diameter (like #57 stone) is ideal. It contains no fine sand or dust, leaving large gaps for water to flow through easily.
Why can't I use crusher run or pea gravel for drainage?
Crusher run contains fine stone dust that packs tightly and blocks water flow. Pea gravel consists of small pebbles that can slip into perforated pipes and clog the drainage holes. You should use clean, washed angular aggregate.
What is a French drain?
A French drain is a trench filled with gravel and a perforated pipe that redirects surface water and groundwater away from an area (like a home foundation) to a safe discharge point.
Do I need to wrap the trench in landscape fabric?
Yes, wrapping the drainage gravel zone in non-woven geotextile landscape fabric is critical. It prevents mud, silt, and soil from washing into the gravel gaps and clogging the drain over time.
How much drainage gravel do I need if there is a pipe in the trench?
A standard 4-inch perforated drain pipe takes up about 0.1 cubic feet of volume per linear foot. For a 50-foot trench, the pipe occupies about 5 cubic feet of volume. You can subtract this from the calculated soil volume if you want to be extremely precise.