French Drain Materials Calculator (Gravel, Pipe & Fabric)

Enter a trench length, width, and depth. We compute the gross trench volume, subtract the pipe displacement (the volume the perforated pipe occupies inside the trench), add a waste buffer, then convert to weight using the gravel's bulk density.

trench volume:
  cu ft = length_ft x (width_in / 12) x (depth_in / 12)

pipe displacement:
  cu ft = pi x (OD_in / 2 / 12)^2 x length_ft

net gravel volume:
  cu ft = trench cu ft - pipe cu ft
  cu yd = cu ft / 27

order volume (with waste):
  order cu yd = net cu yd x (1 + waste%)

gravel tonnage:
  weight_lb   = order cu yd x density (lb/yd3)
  US short tons = weight_lb / 2000

pipe length:
  = trench run length (add any outlet or daylight run and fittings separately)

fabric area:
  wrap width = (width + 2 x depth + 2 x overlap) / 12   (ft)
  fabric sq ft = wrap width x length
  fabric sq yd = fabric sq ft / 9

Named-material densities (lb/yd³): Crushed Stone #57 2,431 · Pea Gravel 2,565 · River Rock 2,835 · Dense-Graded Base / DGA 3,374 (single-point values from CalculatorSoup; pick Custom to enter your own).

The pipe displacement makes this calculator distinct from a general gravel and stone calculator, which multiplies footprint by depth with no pipe inside the trench. For the broader landscape job that wraps around the drain, the topsoil calculator sizes the soil or sod cap above the gravel, and the landscaping estimate calculator rolls materials, labor, and markup into one quoted total.