Calculate how much rock you need in tons and cubic yards for any area and depth, plus coverage, cost, and truck load estimates.
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Rock Formula
A rock calculator works in three directions. The core relationship is volume equals area times depth, with weight found from the rock’s bulk density.
To find the rock needed for a project:
Cubic Yards = (Area * Depth) / 27
Tons = Cubic Yards * Density
To find the area a known quantity of rock will cover:
Area = (Cubic Yards * 27) / Depth
To find the depth a known quantity will reach over a set area:
Depth = (Cubic Yards * 27) / Area
Where:
- Cubic Yards is the loose volume of rock (yd³).
- Area is the project surface area in square feet.
- Depth is the finished rock layer thickness in feet.
- Density is the bulk weight of the rock in short tons per cubic yard.
- 27 is the number of cubic feet in one cubic yard.
The calculator first converts your depth to feet, since area is in square feet, then multiplies area by depth to get cubic feet and divides by 27 to get cubic yards. Multiplying cubic yards by the density of your chosen rock type gives the weight in tons. The same equation rearranges so you can solve for coverage or possible depth instead of quantity. The advanced options apply an overage percentage and a compaction allowance to the volume before pricing, and convert the result into bags or truck loads.
Rock Coverage and Density Reference
One short ton of rock spread evenly covers the following areas. Use it as a quick check against the calculator output.
| Depth | Coverage per ton |
|---|---|
| 1 inch | about 240 sq ft |
| 2 inches | about 120 sq ft |
| 3 inches | about 80 sq ft |
| 4 inches | about 60 sq ft |
| 6 inches | about 40 sq ft |
Different rock types weigh different amounts, which changes how many tons you order for the same volume. These are planning midpoints; confirm the exact figure with your supplier.
| Rock type | Approx. density (tons/yd³) |
|---|---|
| Pea gravel | 1.38 |
| Rock, 2 to 6 in | 1.25 |
| Crushed stone | 1.50 |
| Gravel, ¼ to 2 in | 1.55 |
| Riprap | 1.85 |
Example Problems
Example 1: Rock needed for a bed. You have a rectangular bed 20 ft long and 10 ft wide, and you want 3 inches of ¼ to 2 in gravel at a density of 1.55 tons per cubic yard.
- Area = 20 × 10 = 200 sq ft
- Depth = 3 in = 0.25 ft
- Cubic Yards = (200 × 0.25) / 27 = 1.85 yd³
- Tons = 1.85 × 1.55 = 2.87 tons
You need roughly 1.85 cubic yards, or about 2.87 tons, before any overage.
Example 2: Coverage from rock on hand. You have 5 tons of crushed stone (1.50 tons per cubic yard) and want a 2 inch layer.
- Cubic Yards = 5 / 1.50 = 3.33 yd³
- Depth = 2 in = 0.1667 ft
- Area = (3.33 × 27) / 0.1667 = 540 sq ft
That quantity covers about 540 square feet at 2 inches deep.
FAQ
How many tons of rock are in a cubic yard?
It depends on the rock type. Most landscape gravel and crushed stone run about 1.25 to 1.55 tons per cubic yard, while heavier riprap can reach 1.85 tons per cubic yard. The calculator uses the density of the rock type you select, or your own custom value, so the tonnage matches your material.
How much extra rock should I order?
Add 10 to 15 percent for spillage, uneven ground, and settling. If the rock will be compacted, add more on top of that. The advanced options let you enter both an overage percentage and a compaction allowance so the final quantity reflects what you will actually buy.
What depth of rock do I need?
A decorative top layer is usually 2 to 3 inches deep. For driveways, drainage, or areas that carry weight, plan on 4 inches or more, often in multiple layers. Deeper layers use more rock per square foot, so confirm the depth before ordering.
