French Drain Gravel Calculator
Calculate the volume of gravel needed for a French drain trench.
Enter trench length, width, and depth to get total cubic yards, cubic meters, and weight estimates.
A French drain is a gravel-filled trench with a perforated pipe that redirects groundwater away from problem areas like foundations, yards, and basements. The key material is the gravel — it must be coarse enough to allow free water movement while preventing fine soil from clogging the system.
French Drain Construction
A standard French drain consists of:
- A trench, typically 12–24 inches wide and 18–36 inches deep
- A layer of landscape fabric (geotextile) lining the trench
- A 3–6 inch bed of gravel at the bottom
- A perforated pipe (4-inch diameter is most common)
- Gravel filling the rest of the trench (leaving 2–3 inches for topsoil)
- Landscape fabric folded over the top
- Topsoil or sod to finish
Choosing the Right Gravel
- #57 crushed stone (¾ inch): The most common choice. Good void ratio, large enough to resist clogging.
- #4 crushed stone (1.5 inch): Better for high-flow areas; rarely clogs.
- Pea gravel (⅜ inch): Smooth; flows well but can compact over time.
- River rock: Aesthetically pleasing if used as a surface drain; heavier.
Never Use:
- Fine gravel or sand — clogs rapidly
- Limestone — can dissolve and compact
- Decomposed granite — settles into fine particles
Volume Calculation
The trench is a rectangular prism: Volume (ft³) = Length (ft) × Width (ft) × Depth (ft) Volume (yd³) = Volume (ft³) ÷ 27
Metric: Volume (m³) = Length (m) × Width (m) × Depth (m)
Gravel Weight
Crushed stone weighs approximately 2,700 lbs per cubic yard (1,600 kg per m³) when loose.
Note: Subtract the volume of the perforated pipe from your total if calculating precisely — for a 4-inch pipe in a long trench, this is typically 2–3% of total gravel volume.