Landscape rocks function as both a decorative addition and alternative to mulch in your gardens. Choosing rock for garden surfaces provides a permanent feature that won't break down like normal shredded hardwood mulch. Landscape rock comes in a variety of sizes from pea-sized pebbles to boulders. Learning how to measure landscape rock involves determining the total area of your garden and then deciding on the appropriate depth of the rock bed.
Measure the length and width of the garden in feet and note this on paper. For irregularly-shaped gardens, take general length and width measurements. Measure the length and width of bump-outs or extensions separately as triangles, circles or squares and note these measurements on your paper.
Determine the total square footage by multiplying the length times the width of the garden. Figure any extra areas requiring landscape rocks and multiply length by width for these areas, too.
Add all final figures together to determine the square footage of the garden area.
Decide the appropriate depth of the landscape rock need for the planting area. The standard application of rock allows for a depth of 2 to 3 inches throughout the garden bed.
Understand basic landscape measurement units. One bag of rock will cover a 4-foot-square area with 3 inches of rock. A ton of rock covers a 3-inch-deep, 70-foot-square area. Material also comes in cubic measurements that fill a 3-foot cubed area. This cubic yard of material translates to cover a 250-square-foot area with 1 inch of landscape material. If you want to cover the 250-foot area with 2 inches of rock, you'd double the measurement to 2 cubic yards. Three inches of rock would be 3 cubic yards.
Take your square footage total and divide by the appropriate material measurement. For example, divide total square footage by four to determine the number of bags needed or divide the total square footage by 70 to determine tons of rock required. Divide the total square footage by 250 to determine cubic measurements.
Check your figures using an online landscape material calculator to ensure accuracy. See additional resources for more information.