Gravel Calculator for Concrete Slab Bases
A concrete slab needs 4–6 inches of compacted gravel base under it — about 1.2 cubic yards per 100 square feet at 4 inches, and 6 inches under anything driven on.
Work out what you need
Measure the area, set the depth, and this converts it to cubic yards, 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 — gravel after heavy rain runs to about 105% of its dry weight. The delivered range starts from a published $25–80 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 concrete slab base? The gravel guide covers every other job.
Why 4–6 inches for a concrete slab base
The base is there for even support and drainage, not strength. A slab poured on soil that settles unevenly cracks over the soft spot, however thick the concrete.
What goes wrong
Run the base about six inches past the slab edge and compact it in two or three inch lifts. A base that only reaches the forms leaves the edges unsupported.
Washed stone with the fines screened out never binds. It looks cleaner in the yard and rolls out from under the tyres on the first hill.
Gravel by the numbers
| Weight per cubic yard | 2,800–3,000 lb dry |
|---|---|
| Tons per cubic yard | about 1.5 |
| 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 | cubic yard |
| Typical delivered price | $25–80 per cubic yard |
Road-base gravel carries fines that bind when compacted, which is what makes a driveway hold rather than scatter.