What Size of Rocks Are for a Driveway?

Pea Gravel

• Pea gravel is a decorative rock chosen for its smooth, round shape. It comes in small and large sizes measuring 1/8 to 1/4 inch and 1/2 to 1 1/4 inches, respectively. Due to its shape, pea gravel doesn't stabilize when compacted, so it should not be used to build a driveway foundation. If you want to add style to a gravel driveway, use small pea gravel over compacted, irregularly shaped rocks. Large pea gravel is typically used for garden borders or inorganic mulch.

Small

• Small landscape rocks measure 1/8 inch or less, and contain small particles broken down into a dust-like consistency. The small rocks and dust can compact into a nearly solid layer. It's used as a base for concrete, pavers and other hard surfaces in well-drained soil. For a rock driveway, mix small and medium gravel for a water-permeable surface with visual variation.Avoid using small gravel in an area with poor drainage, as the dense material doesn't allow room for underground moisture to escape.

Medium

• Medium gravel refers to 3/4-inch crushed rocks. The is the size of rock typically used for foundations, because the irregular shapes and sharp edges wedge into each other for a firm base that absorbs tension while leaving enough gaps for water to drain. Rock driveways have a depth of about 12 inches. While you can use medium gravel for the entire driveway, laying it beneath small gravel results in a smoother, more stable driveway.

Large

• Large gravel ranges between 1 and 2 1/2 inches, or about the size of a golf ball. Large, irregularly shaped gravel compacts down, but its larger size doesn't stabilize as well as medium gravel. Use large rocks for the base layer of a driveway if the area has poor drainage. Dig the depth of the foundation to about 12 inches and fill 4 inches with large gravel to help facilitate drainage and prevent smaller rocks from sinking.