French Drain Gravel Calculator

Size the washed gravel, pipe, and fabric for a french drain trench.

Inputs
ft
in
in
Results update as you type — no submit
ResultsLIVE
Washed gravel
3.53 tons
= 2.6 cu yd washed stone
Perforated pipe
50 ft
4 in perforated
Perforated pipe50 ft
Filter fabric200 sq ft fabric
Trench volume2.8 cu yd trench
Formula
gravel = trench 2.8 cu yd − pipe = 2.6 cu yd
weight = 2.6 cu yd × 1.35 tons/yd³ = 3.53 tons
Diagram — trench sectionNTS
12″18″4 INDRAIN SECTION · FABRIC-WRAPPED
MeasureShedmeasureshed.com/calculator/french-drain-calculator
French drain — material listUNITS: FT/IN · SCALE: NTS
Inputs
Trench length50 ft
Trench width12″
Trench depth18″
Pipe4 in
Results
Washed gravel3.53 tons (2.6 cu yd)
Perforated pipe50 ft
Filter fabric200 sq ft
Trench sectionNTS
12″18″4 INDRAIN SECTION · FABRIC-WRAPPED
Shopping list
☐ 3.53 tons washed drainage stone (2.6 cu yd)
☐ 50 ft of 4 in perforated pipe
☐ 200 sq ft filter fabric
Formula
gravel = trench 2.8 cu yd − pipe = 2.6 cu yd
weight = 2.6 cu yd × 1.35 tons/yd³ = 3.53 tons
Estimates for planning only — verify before purchaseSHEET 1 OF 1
How it works

A french drain is a gravel-filled trench that carries water away from a wet spot, usually around a perforated pipe wrapped in filter fabric. The gravel is the material you buy by the yard and the ton, and this calculator sizes it. It multiplies the trench length by its width and depth to get the trench volume, subtracts the volume the pipe takes up, and converts what remains to cubic yards and tons of washed stone.

Washed drainage stone weighs about 1.35 tons per cubic yard, so the tonnage tracks the gravel volume directly. The tool also reports the run of perforated pipe — simply the trench length — and the area of filter fabric needed to line the trench bottom and both walls before the stone goes in.

Use clean, washed stone rather than crusher fines: the open spaces between washed stones are what let water move. Wrapping the stone and pipe in fabric keeps soil from silting up those spaces over time.

Worked example
Trench 50 ft long · 12″ wide · 18″ deep · 4″ perforated pipe
trench = 50 × 1 × 1.5 = 75 cu ft = 2.78 cu yd
gravel = trench − pipe = 2.62 cu yd → 2.62 × 1.35 = 3.53 tons
Questions from the trench
Multiply trench length by width by depth for the volume, subtract the pipe, and convert to yards. A 50 ft trench 12 in wide and 18 in deep with a 4 in pipe needs about 2.6 cu yd, roughly 3.5 tons of washed stone.
Estimates for planning only — verify before purchase
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