River Rock Calculator for French Drains
River rock backfills a french drain 12–18 inches deep — about 0.5 cubic yards per 10 feet of a 12-inch-wide trench, and it has to be washed.
Work out what you need
Measure the area, set the depth, and this converts it to tons, what it weighs on the truck, how many bags that replaces, and roughly what it should cost delivered.
Weight is quoted as a band because moisture moves it more than grade does — river rock after heavy rain runs to about 105% of its dry weight. The delivered range starts from a published $40–200 per cubic yard and is scaled by how your region's material prices compare with the national average, so treat it as a sanity check and not a quote.
Get a real price from yards near youNot a french drain? The landscape rock guide covers every other job.
Why 12–18 inches for a french drain
The drain works on the void space between stones, so the rock has to be washed and uniform — fines are the one thing that will clog it.
What goes wrong
Wrap the trench in filter fabric before the stone goes in. Skip it and silt migrates into the voids, and a drain that silts up cannot be unclogged.
Deeper than about two inches it walks underfoot and spreads. It needs edging, and on any slope it ends up at the bottom of the slope.
River Rock by the numbers
| Weight per cubic yard | 2,400–2,700 lb dry |
|---|---|
| Tons per cubic yard | about 1.3 |
| Bags in a cubic yard | 54 × 0.5 cu ft bags |
| Half-ton pickup, one trip | about 0.25 cubic yards |
| Usually priced by the | ton |
| Typical delivered price | $40–200 per cubic yard |
Tumbled and rounded, so it never locks together. Yards sell it by the ton more often than the yard, and a ton is roughly 0.75 yards.