Gravel Driveway Calculator

Why a driveway is three calculations, not one

A gravel driveway that lasts is not one layer of stone. It is a coarse base that bridges soft ground and drains, a binding middle course whose fines lock the structure together, and a finished top layer that is comfortable to drive on and can be replaced when it wears. Each layer is a different material at a different depth, which is why this calculator runs three separate quantities and adds them.

Skipping the layered build is the most common and most expensive shortcut in gravel work. A single deep layer of one stone either fails to drain or fails to compact, and either way the driveway develops ruts and potholes within its first year.

Compaction is what makes it work

A plate compactor transmits force only a few inches down. Spread ten inches of stone and compact once and you get a firm crust over a loose, unconsolidated mass — it looks finished and it fails quickly. Build in lifts of no more than four inches, and compact each one before the next goes down. Two-inch lifts are better still.

Renting a plate compactor costs about $70 to $110 a day and is the highest-value line item in a DIY driveway build. The full sequence is in the driveway build guide.

Drainage decides the lifespan

Water is what destroys gravel driveways. Crown the surface so the centre sits about 2% higher than the edges — roughly an inch and a half of rise across a twelve-foot width — so rain sheds sideways instead of running along the driveway and washing out the fines. On slopes above about 8%, add cross-drains every fifty to a hundred feet.

Fabric is cheap insurance

Woven geotextile between the subgrade and the base stone costs around $0.45 per square foot and prevents the single failure mode that forces early rebuilds: stone migrating down into soft soil until the driveway effectively disappears. Over clay or anything that holds water, it is not optional. Size it with the landscape fabric calculator.

Width and geometry

Ten to twelve feet is standard for a single vehicle, and twenty to twenty-four where two cars need to pass or park side by side. Add two feet through curves so tires do not drop off the edge and undercut the shoulder. For loops and curved runs, measure along the centreline and use the circular driveway calculator — measuring an edge will give you the wrong area.