Key Takeaways
- Four numbers determine your gravel order: area, depth, density, and allowance
- Measure length times width for area, then multiply by depth for volume
- Most gravel sits between 1.3 and 1.5 tons per cubic yard; use your supplier’s figure
- Add 10 percent FHWA allowance for spillage, uneven ground, and compaction
- The gravel calculator handles all five steps automatically
Cubic yard is a unit of volume equal to a cube measuring 3 feet on each side, commonly used in the US for ordering gravel and other aggregates.
Density in gravel calculations refers to the weight of material per unit volume, typically measured in tons per cubic yard or tonnes per cubic metre.
Four numbers get you there: an area, a depth, a density, and an allowance. Multiply the first two for a volume, multiply that by the third for a weight, add the fourth so you do not come up short. Everything else on this page is detail on getting each of those four numbers right, because that is where gravel orders actually go wrong, not in the multiplication.
Step 1: measure the area
Measure the length and width of the space in feet, and multiply them. A driveway that is 40 feet long and 12 feet wide is 480 square feet. If the shape is not a plain rectangle, split it into rectangles, triangles or a circle, work out each piece, and add them together. A path that runs 30 feet long and then turns a corner for another 10 feet is two rectangles, not one.
If you already know the square footage from a survey or a listing, you can skip the measuring entirely and enter that figure directly.
Step 2: decide the depth
Depth is where the biggest ordering mistakes happen, because it multiplies straight through to the final tonnage. Two inches against three inches is not a fifty percent difference in appearance, it is a fifty percent difference in what you pay.
[PERSONAL EXPERIENCE] As a starting point, decorative gravel over a path or bed usually sits 2 to 3 inches deep. A driveway surface is often 2 to 4 inches over a compacted base that is considerably deeper. A drainage trench commonly runs 12 to 18 inches Asphalt Institute. These are common practice, not a specification: what a particular job needs depends on the soil underneath it, the climate, and what it has to carry, so treat them as a place to start rather than a rule to follow.
Step 3: convert to a volume
Area in square feet times depth in feet gives cubic feet. Depth is usually easier to think of in inches, so divide the inch figure by 12 first. At 480 square feet and 3 inches, that is 480 times 0.25, which is 120 cubic feet.
Divide by 27 to get cubic yards, because a cubic yard is 27 cubic feet exactly. 120 divided by 27 is about 4.44 cubic yards. This is the number a supplier who sells by the yard wants.
Step 4: turn the volume into a weight
Multiply cubic yards by the material’s density in tons per cubic yard. Most crushed stone and gravel sits between 1.3 and 1.5 tons per cubic yard, with 1.4 being the figure quoted most often for a washed stone such as #57. At 4.44 cubic yards and 1.4 tons per cubic yard Aggregate Industries, that is about 6.22 tons.
Density is not a universal constant. It is a property of the specific material, and it is worth using your supplier’s own figure once you have one, because it describes the pile you are actually buying rather than a published average. Our material density reference lists the typical figures for common gravel types.
Step 5: add an allowance
Add 10 percent or so before you order. Spreading and grading lose material at the edges, the ground is never perfectly flat, and a compacted layer needs more material than its finished depth suggests, because loose gravel settles. At 6.22 tons and a 10 percent allowance, that comes to about 6.84 tons, which rounds up to whatever increment your supplier sells in.
Doing all of this at once
That is five steps and five separate calculations, which is exactly the amount of arithmetic a gravel calculator exists to remove. Enter the same length, width, depth, material and allowance, and it returns the tons, cubic yards, cubic metres and bag count together, with the same working shown line by line so you can check it against your own numbers.
For a project built in layers, such as a driveway with a sub base, a base and a surface course, the driveway calculator runs each layer through the same five steps separately and adds the results, which a single average depth cannot do accurately. And once you have a tonnage, the cost calculator and the bag calculator carry the same numbers through to what it will actually cost and how many bags to carry, so you never have to start the arithmetic over for a different question.
Editorial note: This article is reviewed for accuracy and updated regularly. All calculations use standard industry formulas. For the latest density figures, consult your gravel supplier directly.
Frequently asked questions
How do I calculate how much gravel I need?
Measure the length and width in feet and multiply for square footage. Multiply by the depth in feet (divide inches by 12) for cubic feet. Divide by 27 for cubic yards. Multiply by the material’s density (typically 1.4 tons per cubic yard) for weight. Add 10 percent for waste.
What depth should I use for my project?
Decorative beds and paths: 2 to 3 inches. Driveway surfaces: 2 to 4 inches over a compacted base. Drainage trenches: 12 to 18 inches. These are starting points; your soil, climate, and load requirements may need more.
How much extra should I order?
Add 10 percent to your calculated amount. This covers spillage during spreading, uneven ground, and the fact that loose gravel settles when compacted. For projects on soft soil or with tight access, consider 15 percent.
Should I use my supplier’s density or the published average?
Always use your supplier’s density if they provide it. Published averages are starting points, but the actual material you buy can vary by 10 percent or more depending on the parent rock, moisture, and grading.