Pea gravel comes in various sizes and types. Particle size can vary from a small and uniform ¼-inch diameter to an oblong shape that is from ½ to ¾ of an inch. Most suppliers will give an approximate fill capacity in cubic feet per ton of gravel. The most general consensus of coverage is 100 square feet at a 2-inch depth. Using this amount of coverage, the typical weight of pea gravel is a ton of material.
Consult with the local supplier to find the density of the pea gravel product. In general, a ton, or 907kg., will cover 100 square feet at a 2-inch depth. A hundred square feet is equal to a uniform square that is 10-by-10 feet.
Find the amount of cubic footage used in the above example. Divide the 2-inch depth by 12 inches to find the amount of feet contained in the 2 inches. The result is 2 divided by 12 (2/12), which is equal to 0.167 feet. Multiply 0.167 feet times 100 square feet to find the cubic footage of a ton of pea gravel with the density described in Step 1. The answer is 16.7 cubic feet.
Calculate the cubic yardage of the pea gravel product using the same density. A cubic yard of material is equal to a cube that measures 3 feet wide by 3 feet long and 3 feet deep. Multiply all three measurements together--a cubic yard contains 27 cubic feet of material. Divide the 16.7 cubic feet by 27 cubic feet per cubic yard. The result is 0.61 yards of material that is needed to cover a 10-by-10-foot square 2 inches deep.
Find the coverage area of 1 full cubic yard of the same material at a 2-inch depth. From Step 2, divide 16.7 cubic feet into 100 square feet to find the amount of gravel that will cover a single square foot. The result is 0.167 cubic feet. Divide the 0.167 cubic feet by 27 cubic feet per yard to get 161.7 square feet that can be covered by 1 full yard of the pea gravel. In other words, 1 cubic yard will spread out to a rectangle that measures 10 feet wide by approximately 16 feet long and 2 inches deep.
Understand that if the thickness is decreased by half the amount, the pea gravel would then cover twice the area. In other words, if the gravel was spread to a 1-inch thickness, it would cover approximately 320 square feet, or a 10-by-32-foot rectangle.
Finding an exact size and amount of pea gravel coverage is not perfect. There are many variations in the size of the product, and only a rough estimate can be calculated. It may always be better to over-order the amount of pea gravel when finding how much the material will spread.