";steps += "1. Convert Depth to Feet: " + d + " in / 12 = " + depthFeet.toFixed(4) + " ft
";steps += "2. Calculate Volume (Cubic Ft): " + l + " x " + w + " x " + depthFeet.toFixed(4) + " = " + volumeCF.toFixed(2) + " ft³
";steps += "3. Convert to Cubic Yards: " + volumeCF.toFixed(2) + " / 27 = " + volumeCY.toFixed(2) + " yd³
";steps += "4. Calculate Tons: " + volumeCY.toFixed(2) + " yd³ x " + density + " tons/yd³ = " + weightTons.toFixed(2) + " tons";if(showSteps){document.getElementById('stepsOutput').innerHTML = steps;document.getElementById('stepsOutput').style.display = 'block';}else{document.getElementById('stepsOutput').style.display = 'none';}}
How to Use the Rock Calculator
Whether you are installing a new driveway, creating a xeriscape garden, or building a drainage pit, our rock calculator helps you determine the exact amount of material needed. Buying too little rock leads to extra delivery fees, while buying too much is a waste of money and labor.
To get the most accurate estimate, follow these steps:
- 1. Choose Material Type
- Select the type of rock you plan to use. Different rocks have different densities; for instance, dense gravel weighs more per cubic yard than porous lava rock.
- 2. Area Length and Width
- Measure the length and width of the coverage area in feet. For irregular shapes, it is best to divide the area into rectangles and calculate each separately.
- 3. Depth in Inches
- Decide how deep you want the rock layer to be. Standard landscaping depth is 2-3 inches, while driveways often require 4-6 inches.
How It Works: The Formulas
The rock calculator uses three primary steps to convert your physical dimensions into a weight measurement (tons), which is how most quarries sell bulk rock.
Volume (yd³) = [(Length × Width × (Depth / 12))] / 27
Once the volume is found in cubic yards, we apply the material density:
Total Tons = Volume (yd³) × Density (tons/yd³)
- Length & Width: Measured in feet to establish the surface area.
- Depth Conversion: We divide the inches by 12 to convert to feet before multiplying.
- Cubic Yard Conversion: Since there are 27 cubic feet in one cubic yard, we divide the total cubic feet by 27.
- Density: Most gravel is approximately 1.4 tons per cubic yard.
Calculation Example
Example: You are filling a decorative garden bed that is 20 feet long and 5 feet wide with river rock at a depth of 3 inches.
Step-by-step solution:
- Convert Depth: 3″ / 12 = 0.25 feet.
- Calculate Area: 20ft × 5ft = 100 square feet.
- Calculate Volume (CF): 100 sq ft × 0.25 ft = 25 cubic feet.
- Convert to Cubic Yards: 25 / 27 = 0.925 cubic yards.
- Apply Density (River Rock = 1.5): 0.925 × 1.5 = 1.39 Tons.
- Result: You should order approximately 1.4 tons of river rock.
Rock Density Reference Chart
| Material | Tons per Cubic Yard |
| Crushed Stone | 1.4 |
| Pea Gravel | 1.45 |
| River Rock | 1.5 |
| Sand | 1.35 |
| Lava Rock | 1.1 – 1.2 |
Common Questions
How many bags of rock equal a ton?
Most standard rock bags from hardware stores weigh 0.5 cubic feet or about 40-50 lbs. There are 2,000 pounds in a ton. Therefore, you would need approximately 40 to 50 bags to equal one ton of rock. For large projects, buying in bulk is significantly cheaper.
Should I account for settling?
Yes. For loose materials like gravel or sand, it is wise to add a 10% "waste factor" to your order. This accounts for material that settles into the soil, fills in gaps, or is lost during the shoveling and moving process.
What is the best depth for a rock driveway?
A stable rock driveway usually requires a base layer of 4 inches of larger "crusher run" rock and a top layer of 2 inches of decorative or smaller gravel, totaling a 6-inch depth for long-term durability under vehicle weight.