French drain stone calculator
Stone quantities from trench size. A typical French drain runs a 6 to 12 inch wide trench, 18 to 24 inches deep, with 4 inch perforated pipe wrapped in fabric and clean stone to within a few inches of grade.
To size a french drain, multiply length by width by depth in feet and divide by 27: that is cubic yards of spoil. Spoil weight has no single right number, but this calculator works from 3/4" clean stone (standard) at about 2,800 lb per cubic yard, roughly 1.40 tons a yard. Soil type and moisture move it more than anything else, and excavated material swells, so it will not fit back in the hole it came out of.
Pro habit: Order about 13.6 yd³; the pipe displaces a little, but settling into the fabric and trench irregularities eat the difference.
Use washed (clean) stone only. Stone with fines clogs, which is how a French drain becomes a buried wet spot. Line the trench with filter fabric, and figure roughly one 4 inch perforated pipe length per foot of drain. Weights are common industry approximations; confirm with your supplier before ordering.
The number above assumes a few things about how this material behaves in the ground.
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Common questions
How do I calculate the volume of a french drain?
Multiply length by width by depth in feet, then divide by 27 to get cubic yards. This french drain calculator does it for you: enter length and width in feet and depth in inches, and it returns cubic yards, estimated tons, and truckloads. Add about 10 percent for compaction, spillage, and uneven grade.
How many tons is a cubic yard of excavated soil?
There is no single number, and anyone who gives you one is guessing. Spoil from a french drain typically runs somewhere around 1.40 tons per cubic yard (3/4" clean stone (standard) at about 2,800 lb/yd³), but soil type and moisture move it more than anything else: dry sand and saturated clay are not close. Weigh a load if the haul-off number matters, and remember excavated material swells, so it will not go back in the same hole it came out of.
Is this french drain calculator free?
Yes. It is a free tool from TrackOver, software built inside a working excavation company for contractors who move dirt. No signup required to use it.
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