The Foundation of Hardscaping
Gravel is the unsung hero of outdoor construction. Whether you are laying a decorative crushed stone driveway, pouring a concrete slab (which requires a compacted gravel sub-base), or building a retaining wall (which requires drainage gravel behind it), estimating the exact volume of stone you need is critical.
Gravel is heavy, hard to shovel, and expensive to deliver. If you order too little, you have to pay a second, exorbitant delivery fee for a dump truck to bring you another scoop. If you order too much, you are stuck with a massive pile of heavy rock in your driveway that you have to somehow dispose of.
Understanding Cubic Yards
Unlike topsoil or mulch which can easily be bought in small plastic bags at the hardware store, structural gravel is almost exclusively ordered "in bulk" from a local quarry or landscape supply yard.
Bulk materials in the United States are sold by the Cubic Yard. A cubic yard is a three-dimensional cube of material that measures 3 feet long by 3 feet wide by 3 feet high. It contains exactly 27 cubic feet.
To visualize this: one cubic yard of gravel is roughly the size of a standard washing machine, and it weighs approximately 2,800 to 3,000 pounds (1.5 tons).
How to Calculate Gravel Volume
Calculating your gravel needs requires finding the three-dimensional volume of your project area (Length × Width × Depth) and then converting that volume into cubic yards.
The Compaction Factor
There is a critical secret to ordering gravel: Compaction. When dump trucks drop gravel, it is loose and full of air pockets. When you spread it and run a heavy steel plate compactor over it, the jagged stones lock together and the air pockets disappear, causing the gravel to "shrink" in depth by up to 15%. If you do not account for compaction, your 4-inch deep driveway will suddenly become 3.5 inches deep after you drive on it.
The Formula
- Keep the Length and Width of your project in feet.
- Convert the desired Depth from inches to feet by dividing by 12. (e.g., 4 inches = 0.33 feet).
- Multiply Length × Width × Depth to find the total Cubic Feet.
- Divide the Cubic Feet by 27 to convert to Cubic Yards.
- Multiply the result by 1.15 to add a 15% factor for compaction and waste.
Total Cubic Yards = ((Length × Width × (Depth ÷ 12)) ÷ 27) × 1.15
Example Calculation
You are building a crushed-stone parking pad for your RV. The pad will be 20 feet long, 10 feet wide, and you want the gravel to be exactly 4 inches deep after it is fully compacted.
- Convert Depth to feet:
4 ÷ 12 = 0.333 ft - Calculate Cubic Feet:
20 ft × 10 ft × 0.333 ft = 66.6 cubic feet - Convert to Cubic Yards:
66.6 ÷ 27 = 2.46 cubic yards - Add 15% Compaction:
2.46 × 1.15 = 2.83 cubic yards
You should call the quarry and order 3 cubic yards of gravel.
Types of Gravel
Make sure you order the correct type of stone for your specific project:
- Crusher Run (or Item 4 / 3/4" Minus): This is crushed stone mixed with heavy stone dust. When compacted, the dust acts like cement, locking the jagged stones together into a rock-hard, non-shifting surface. This is mandatory for driveways and paver bases.
- Washed Stone (or 3/4" Clean): This is crushed stone where all the dust has been washed away. It does not compact or lock together. It is used exclusively for drainage (like French drains or behind retaining walls) because water can flow freely through the empty gaps between the stones.
- Pea Gravel: Small, smooth, round river stones. They feel great underfoot but will never compact. If you use pea gravel for a driveway, your car tires will instantly sink into it like quicksand.