Drainage Trench Materials Calculator

Measure trench section

Use the length, width and gravel-filled depth. Multiply them for trench volume. The calculation assumes a rectangular section throughout.

This planner models a rectangular trench with constant gravel width and depth. Measure its actual route around bends rather than a straight point-to-point distance. Calculate widened sections and chambers separately, then add aggregate. Check ground levels and existing services before excavation: real constraints can change the proposed cross-section.

Subtract the pipe

Use pipe outside diameter to calculate cylinder displacement. The pipe must fit within the entered gravel section.

Pipe displacement uses outside diameter, not nominal size or inside bore. The cylinder occupies π × radius² × length and must fit inside the entered gravel width and depth. Zero diameter can represent a gravel-only trench. For an actual pipe, read OD from its product data rather than guessing from the size in its name.

Default example

A 10 × 0.4 × 0.4 m trench is 1.6 m³. A 0.1 m OD pipe occupies π × 0.05² × 10 ≈ 0.07854 m³, leaving 1.52146 m³ net aggregate. Ten percent allowance gives 1.67361 m³ or 1,673.6 L; at 25 L per bag, buy 67. Fabric spanning a 0.4 m base, two 0.4 m sides and 0.3 m overlap needs 1.5 m developed width along the 10 m run.

Fabric and limits

If fabric is selected, add base, two side walls and overlap, then multiply by length. The roll must be wide enough to span that developed section. This tool does not determine slope, soil infiltration, pipe capacity or outlet.

The chosen fabric roll must span that developed width. Roll count follows trench length divided by roll length; it does not model joining narrow strips or overlap at crosswise seams. Bag quantity is volumetric, not a mass estimate, and rough excavation walls can increase material use. This result does not establish flow capacity, slope, outlet or soil infiltration; those need separate design before building.