The gravel that you apply during the installation of your home driveway won’t just be a single flat layer of pebbles. No matter what the specifications of your project, or what the square footage of your driveway may be, the layer of gravel you put down will have some depth.
Because of the dimension of depth, figuring out how much gravel you need means that you’re looking for a measure of volume and not just square footage. In this case, since gravel is sold in units of cubic yards, you will need to find the volume of material you need, expressed as cubic yards.
If this sounds confusing to you, the math is actually quite simple. However, it’s necessary to go over the language behind the numbers first so that you can execute your project having a full picture of what’s happening.
First, measure the distance of the driveway from front to back in feet, and then measure the width of the driveway, also using feet. Finally, determine the depth of the driveway that will be filled with gravel. The depth will most likely only be a small number of inches.
However, because the other two measurements are being expressed as feet, the depth should be calculated that way as well. For example, if the depth is 3 inches, use a fraction like 1/4 of a foot or decimal like .25 feet for the final calculation. The amount isn’t changing, just the units, as 3 inches is equivalent to a quarter of a foot.
Calculate the Volume
To calculate the volume, multiply the three measurements, length by width by depth. For instance, if you have a gravel driveway that is 36 feet long, 9 feet wide, and 3 inches deep, multiply:
36 x 9 x .25 = 81 cubic feet of gravel
You now know that 81 feet cubed is the amount of gravel you need. That is your volume, and that is a perfectly valid answer mathematically.
Unfortunately, the reality is that in order to actually purchase the proper amount of gravel, that 81 cubic feet will need to be converted into an amount that is exactly equal in quantity but is measured by a different unit.
Convert Cubic Feet to Cubic Yards
Cubic yards is the unit of measure that most retailers use to quantify their gravel. To convert any amount of cubic feet into cubic yards, simply divide by 27, as that is the number of cubic feet that makes up 1 cubic yard. This rule is true for the 81 cubic feet in this example, and it’s also true for whatever volume your individual project yields.
To complete the example, 81 cubic feet divided by 27 comes out to 3 cubic yards, since 81/27 = 3.
Thus, you will 3 cubic yards of gravel for the project.
Tip: In exactly the same way that 3 is the number of non-cubic feet that make up 1 non-cubic yard, and any amount of feet divided by 3 will give you a measurement in yards, 27 is the magic number for these units.
Check Your Math
Just like with all calculations where precision is important, you want to make sure you haven’t made any careless mistakes. Run your numbers again, especially if you weren’t comfortable or confident with the mathematics involved the first time around.
Getting an accurate idea of how much gravel to buy can save you time, money, and strife.