How deep should gravel be for a driveway, patio or path?

There is no single answer, because "gravel" does three different jobs. In a bed it is decoration, on a path it is a walking surface, and under a driveway or a patio it is structure. Depth follows the job, and the sources we could find agree on the broad strokes but not on the details, so this guide shows where they diverge.

Quick reference

All depths are finished and compacted.

Use	Typical depth	Source basis
Decorative gravel in beds	2 to 3 inches	Roseville Rock Supply
Garden path or walkway	3 to 4 inches	Roseville, Harbor Soils
Paver patio base	about 4 inches	Roseville
Under a concrete patio slab	compacted gravel subbase	Quikrete, Concrete Network
Driveway, light car use	4 to 6 inches	Harbor Soils; Culpeper SWCD
Driveway, new build or soft ground	6 inches or more, in layers	Harbor Soils; Culpeper SWCD

Decorative beds and paths

For ornamental rock over landscape fabric, 2 to 3 inches is enough to hide the ground and stop weeds from pushing through. Pathways use a little more, 3 to 4 inches, because feet and wheelbarrows push the stone around. One supplier says a thin walking path of 3 inches is fine as long as it sits on a compacted base.

Choose a stone you will not mind walking on. Pea gravel is rounded and comfortable, but it shifts underfoot. A crushed stone that locks together makes a firmer surface.

Patio bases

Under pavers, supplier guidance is about 4 inches of compacted base rock. The usual material is crusher run or a similar mix of stone and fines, because it compacts into a firm bed. Compact the base in layers, not all at once, and follow the paver manufacturer's installation sheet for your product, since base requirements differ by paver and use.

Under a poured concrete patio, you still want a compacted gravel subbase. Quikrete's patio guide describes a 4 inch slab set about 2 inches above ground and says that where the patio sits more than 8 inches below the door, it should be built up with a thicker crushed stone subgrade rather than thicker concrete.

Driveways

Here the sources part company, and it is worth understanding why.

Harbor Soils (a landscape supplier) treats 4 inches as the standard finish layer for a residential driveway, and 6 inches, as a 3 inch base plus 3 inch top, for a new driveway or heavy loads.
Culpeper Soil and Water Conservation District (Virginia), in its guide for dirt and gravel roads and driveways, says the gravel surface should be at least 6 inches deep, with 6 inches of fine gravel on top and coarse stone like #57 as a base where strength and drainage are needed.
UVM Sea Grant's stormwater-friendly driveway design calls for 12 inches of subbase on well-drained sandy soil and 16 inches on other soils. That is for a permeable design that stores runoff, not for an ordinary gravel drive, so do not take it as a general target.

Our default for a car driveway on decent ground is 6 inches total after compaction, in two layers: a coarse base and a finer top. Go deeper on clay or soft ground. The conservation district's guide shows that rutted, soft soil should be reinforced with geotextile fabric and needs extra surface stone.

Two more points. First, use angular crushed stone for the load-bearing layers, since rounded stone does not lock together. Second, slope matters: Burlington, Vermont's stormwater program recommends against gravel driveways on slopes steeper than 2 percent because the stone washes into the road.

How much stone each depth needs

These figures assume 1.4 tons per cubic yard, a typical crushed stone, per 100 square feet. The right column adds 15 percent for compaction.

Depth	Cubic yards	Tons	Tons with 15% compaction
2 inches	0.62	0.86	0.99
3 inches	0.93	1.30	1.49
4 inches	1.23	1.73	1.99
6 inches	1.85	2.59	2.98

Worked example: a single-car driveway

A driveway 10 ft wide and 40 ft long is 400 square feet. We want 4 inches of coarse base and 2 inches of finer surface stone.

Base: 400 x 4 / 324 = 4.94 cubic yards. With 15 percent for compaction, 5.68 yards, which is about 7.95 tons at 1.4 tons a yard.
Top: 400 x 2 / 324 = 2.47 cubic yards, about 3.46 tons.
Total: about 8.15 cubic yards, or roughly 11.4 tons.

Single-layer, the same 6 inches gives 7.41 cubic yards before compaction. Metric: 3.05 m by 12.2 m (37 square metres), 15 cm deep, about 5.7 cubic metres before the allowance.

Mistakes to avoid

Treating depth as a loose measurement. Stone shrinks as it compacts, and the shrinkage runs 10 to 20 percent according to the two suppliers that gave figures.
Spreading it all in one lift. Thick fills should be compacted in layers. The UVM design, for example, specifies lifts of at least 6 inches, so ask what your equipment can handle.
Using pea gravel or river rock on a slope or in a driveway. The rounded stones roll.
Skipping the base on soft ground. A thin layer of stone without a firm base disappears into the soil.
Forgetting drainage. Shape or crown the surface so water and sediment shed to the sides, as the UVM guide suggests, instead of running down the drive.

When in doubt, call a local supplier. They know the stone, the soil and the frost depth around you. The calculator on the gravel page will convert whatever depth you choose into tons and bags.