Rock needed (tons) = area x depth (ft) / 27 x density (tons per cubic yard). Get cubic yards and tons for river rock, crushed stone, lava rock and more.
Add 5 to 10% overage for waste, cutting, and uneven ground.
Volume (cu yd) = length (ft) x width (ft) x depth (ft) / 27. Tons = cubic yards x density (tons per cubic yard). Convert depth from inches to feet by dividing by 12.
Rock density varies by type. River rock and pea gravel weigh about 1.35 tons per cubic yard. Crushed limestone runs heavier at 1.5 tons per cubic yard. Lava rock is much lighter at around 0.7 tons. The wrong density figure can throw your order off by 30 percent or more. The select menu above uses field-tested values for common landscape rock types.
Two inches is the minimum for decorative coverage in flat, dry areas. Three inches is the standard for most residential landscaping; it blocks most weed growth and stays stable in rain. Four to six inches is appropriate for drainage beds, erosion control on slopes, and high-traffic areas. For larger rock sizes like 3 to 5 inch boulders, consider the void space: larger pieces leave more air gaps, so coverage differs from finer material at the same depth.
If you are ordering fine crushed gravel or road base by the ton, the gravel calculator covers that with cost-per-ton pricing. This rock calculator is better suited for decorative landscape stone, river rock, and coarser material where type-specific density matters. For the full project volume in cubic yards, see the cubic yard calculator.
Area (sq ft) x depth (ft) / 27 = cubic yards. Multiply cubic yards by the density in tons per cubic yard to get tons. River rock runs about 1.35 tons per cubic yard; crushed limestone about 1.5 tons.
River rock and pea gravel: about 1.35 tons. Crushed limestone: about 1.5 tons. Lava rock: around 0.7 tons. Decomposed granite: about 1.4 tons. The rock type selector above uses these values.
At 2 inches deep: roughly 100 sq ft per ton of river rock. At 3 inches: about 70 sq ft. At 4 inches: around 50 sq ft. Lighter rock like lava rock covers more area per ton.
2 to 3 inches for decorative ground cover, 3 to 4 inches for weed suppression, and 4 to 6 inches for drainage or erosion control.
Gravel is a term for small loose stones, usually 1/4 to 2 inches. Landscape rock covers a wider range of sizes and types. Crushed stone is angular; river rock is smooth from water erosion. Both are sold by the ton.
Chris Terry is the editor of Encore Editorial and oversees content, sourcing, and the accuracy of everything published here. His background spans business operations, market research, and making complicated things readable.