Calculation method
The stone estimate is the rectangular stone-filled trench volume less the outside volume of one round pipe. Pipe length equals the measured run. Fabric area uses the entire trench wrap perimeter plus an entered top lap. This is a material estimate, not a drain design or a hydraulic capacity calculation. For a route with changing trench size, divide it into measured segments and sum their individual material quantities. Check the actual outside pipe diameter, the portion of trench filled with stone, roll widths, seams, and supplier order increments before buying.
Worked example: inputs to material quantity
For a 60 ft run, 12 in wide and 18 in deep trench, 4 in outside-diameter pipe, 6 in fabric lap, and 10% extra stone: stone is about 3.45 yd³, pipe is 60 ft, and fabric covers 330 ft² before seams.
What the estimate covers
All dimensions are user-entered. Round quantities and order sizes against your supplier’s current stock; the page does not design structural, drainage, or suspension systems. The related guide explains each assumption and common measurement mistakes.
Product and method reference
The external source offers installation or measurement context; the arithmetic and illustrative defaults here are stated separately. NDS drainage planning and French drain context.
Calculation and editorial review: November 3, 2026. Arithmetic runs in your browser; project inputs are not submitted to TwoCut.