How Deep Should Gravel Be? Recommended Depths for Every Project

Depth is the number that drives a gravel order. Double the depth and you double the tons. Too thin and the soil shows through or ruts appear; too thick and loose stone feels like walking on a beach and costs more than necessary. These recommendations reflect common landscaping practice; adjust for your soil and how the area will be used.

Recommended depths at a glance

Project	Surface stone	Base layer	Total
Decorative bed (stone mulch)	2–3 in	none (fabric optional)	2–3 in
Garden path	2–3 in	2–4 in compacted base on soft soil	2–7 in
Pea gravel patio	3–4 in	3–4 in compacted base	6–8 in
Shed or hot tub pad	2 in	4–6 in compacted crushed stone	6–8 in
Residential driveway	2–3 in	6–8 in in two layers	8–12 in
Under a concrete slab	—	4 in compacted	4 in
French drain	fill trench around pipe	2–3 in under the pipe	trench depth

Why a base layer matters

Surface gravel on bare soil works for decorative beds, but anything you walk or drive on needs a base. Without one, the stone is pushed down into the soil, mud pumps up through the gaps, and within a season you have a muddy path with a few stones in it. A compacted layer of angular crushed stone with fines spreads the load and stops that mixing. On clay soil, a geotextile fabric under the base adds insurance.

Why surface layers stay thin

It is tempting to add more surface stone "to be safe," but loose surface stone deeper than about 3 inches becomes hard to walk on, pushes around under tires and makes wheelbarrows and strollers struggle. Strength comes from the compacted base, not from a thick loose top.

How much does each inch cost?

For every 100 square feet, each inch of depth adds about 0.31 cubic yards, roughly 850–900 lb of typical gravel. On a 600 square-foot patio, the difference between 3 and 4 inches of pea gravel is almost two cubic yards, about 2½ tons. Use the gravel calculator to compare depths before you settle on one.

Area	2 in	3 in	4 in	6 in
100 sq ft	0.62 yd³	0.93 yd³	1.23 yd³	1.85 yd³
300 sq ft	1.85 yd³	2.78 yd³	3.70 yd³	5.56 yd³
600 sq ft	3.70 yd³	5.56 yd³	7.41 yd³	11.11 yd³

Stone size and depth

A layer should be at least two to three times as deep as the largest stones in it. One-inch river rock spread a single inch deep leaves gaps of soil between the stones; at 2–3 inches it forms a continuous layer. For large decorative rock of 2–4 inches, plan on 4 inches or more, or accept a sparser, more natural look.

Measuring depth during installation

Drive stakes and mark the finished height with a string line or paint.
Use a short stick marked at the target depth to check as you rake.
Compact each base layer before adding the next; a 4-inch loose layer may compact to around 3 inches, so check depth after compaction.

Topping up later

Paths and driveways lose stone over time as it migrates, gets plowed into the lawn or sinks. Plan on adding a thin top layer every few years. An inch over 500 square feet is about 1.5 cubic yards. For mulch-style decorative beds, see also our cubic yard guide on measuring irregular areas.