Gravel-Coverage Calculations
- Plan on excavating your driveway or parking area to a depth of about 6 inches. Remember to create a proper slope and/or crown for drainage and build in ditches. Also, there may be codes and regulations in your county or community. Once you have the area excavated, spray a herbicide, then lay down a landscaping fabric, sometimes called weed-barrier fabric. You don't want weeds or grass growing through your gravel driveway. Install 4 inches of standard gravel. Drive over it with heavy equipment and allow it to settle a bit. Then add 2 inches of clean, decorative gravel. Over time, you may need to add gravel to account for settling.
- Landscaping will obviously get a lot less traffic than a driveway or parking area. But controlling water coming into the landscaped area and drainage are two important factors. This is important whether the landscaping abuts the foundation of a home, runs along a drive or is in the middle of a yard. You'll need landscaping fabric, which allows water and nutrients to reach the soil but won't allow weeds or anything else to sprout through your gravel. You can transplant trees, shrubs or plants, but do not grow them from seed. Landscaping fabric will break down if exposed to the sun's UV rays, so you need to cover it completely. Lay down 3 inches of rock to keep the barrier effective. Since gravel is often made up of larger stones, you might consider laying down a thinner layer of smaller stones first, then adding the gravel on top.
- If you're using two different types of stones, you'll need to do two separate calculations. Both use the same volume calculation, which is: length x width x depth (in feet) = cubic feet divided by 27 = cubic yards. One cubic yard equals 27 cubic feet (3 feet x 3 feet x 3 feet). A sample calculation looks like this: 200 feet x 30 feet x .33 (4 inches) = 1,980 cubic feet/27 = 73 cubic yards. Note: when you have decimals in your final number, round up or down depending on your needs.
- For circular areas, you'll need to adjust the calculation. First, find the radius of the area. Radius is 1/2 of the diameter. Then, take the radius squared x 3.14 (Pi) x depth. This will give you the number of cubic feet. Divide that number by 27 and the resulting number will be the cubic yards you'll need. A sample calculation for a 25-foot diameter circle that's 6 inches deep will look like this: 12.5 x 12.5 (the radius squared) x 3.14 x .5 (6 inches) = 245 cubic feet/27 = 9 cubic yards.
