Gravel is commonly used for driveways, as a subsurface for brick or concrete paver patios and as decoration for landscaping projects. It's a durable and cost-effective material for all of these uses, but it's important that you measure and calculate gravel accurately. If the gravel is needed for a new driveway or other project, excavate the area before measuring and calculating the amount of gravel needed, to make sure you correctly estimate the depth required.
Measure the length and width of the area where gravel is to be poured. Multiply the length by the width to find the area, or square footage. For example, a driveway that is 180 feet long and 10 feet wide is 1,800 square feet. For longer distances, rent a measuring wheel from a tool rental or home-improvement store, rather than trying to use a tape measure.
Measure the depth of gravel required in inches. This will vary depending on the type of project and whether you are building new or resurfacing an existing gravel bed. For example, a new driveway might need a 12-inch base, but only 3 inches of gravel may be required for resurfacing.
Convert the depth in inches to a fraction of a foot in decimal form by dividing the depth by 12. For example, a 3-inch layer of gravel is 3 / 12 = 0.25 feet.
Multiply the square footage by the depth to find the volume in cubic feet. An area of 1800 square feet that requires a gravel layer 0.25 feet deep needs 450 cubic feet of gravel.
Convert cubic feet into cubic yards. This is necessary because gravel is most often sold by the cubic yard. There are 27 cubic feet in a cubic yard, so divide the cubic feet by 27. For example, 450 cubic feet divided by 27 works out to 16.67 cubic yards of gravel.
Multiply the cubic yards of gravel needed by 1 3/8 (1.375 in decimal form) to find the tons of gravel required. You'll need to do this conversion if your supplier is among those selling by weight instead of volume.
16.67 x 1.375 = 22.92
You need 23 tons of gravel, after rounding up.
To find the square footage of a circular area, square the distance from the centre to the edge (the radius) and multiply by 3.14 (pi). For curved sections of walkway or drives, measure the inside and outside edge of the curved section. Add the two measurements together and divide by 2 to find the average length of the curved section.