How to Estimate Landscaping Materials

When landscaping a backyard or garden, it is important to accurately estimate the amount of topsoil, mulch, sand, and gravel needed to maintain a vibrant lawn or garden. Making these simple calculations will help you purchase the right amount of landscaping materials. This means you can avoid running short of materials or having too much left over.

First, determine the square footage of the area to be landscaped. For a rectangle, area is equal to length times width. For a triangle, area is equal to 1/2 times base times height. And for a circle, area is 3.1416r², where r is the radius.

For outdoor areas that are irregular shapes, and sections on a slope, you can get the most accurate estimate by partitioning the lawn into smaller rectangles and triangles. Use a measuring tape to find the dimensions and square footage of each smaller area, then add these areas to arrive at the total square footage. Don't forget to subtract the area of sheds and outbuildings.

Now, take the total square footage found above and multiply it by the depth (in inches) of mulch, soil, sand, or gravel. For example, if the lawn has an area of 1100 square feet, and the soil is to be laid 3 inches deep, then we get 3300.

Lastly, divide this number by 324 to obtain the cubic yards. (Why 324? There are 3 feet to a yard and 36 inches to a yard. So when you have feet² times inches, you need to divide by a factor of 3*3*36 = 324.)

For example, since 3300/324 = 10.2, you will need to purchase about 10.2 cubic yards of topsoil or other material.

For sand and gravel, you may need to multiply the cubic yards by a density factor to convert the volume to tons. Here are the densities of two common materials:

Dry Sand: 1.284 tons per cu. yd.
Dry Gravel: 1.351 tons per cu. yd.

For example, if you calculate that you need 6 cubic yards of sand to landscape your lawn, then you must purchase about 6(1.284) = 7.7 tons of sand.

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