Decomposed Granite Calculator: How Much Do You Need?

This calculator determines the volume of decomposed granite (DG) you need for a project in cubic yards and cubic feet. You enter the length, width, and desired depth of the area, and it returns the amount of DG required. This is the essential first step before ordering, as DG is sold by the cubic yard.

Formula

The calculator uses the basic volume formula for a rectangular prism: Volume = Length × Width × Depth. The inputs are in feet and inches, so the formula converts them to a single unit before calculating.

• L = length of the area in feet (ft)
• W = width of the area in feet (ft)
• D = depth of DG in inches (in)

To get cubic yards, the formula is: (L × W × (D/12)) / 27. This is simplified to L × W × D / 324 because 12 × 27 = 324. To get cubic feet, it is L × W × (D/12), simplified to L × W × D / 12.

Worked Example

Using the default values from the calculator: a 40 ft long by 25 ft wide area with a 3-inch depth.

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Calculate volume in cubic feet: 40 ft × 25 ft × 0.25 ft = 250 ft³
3. Convert to cubic yards: 250 ft³ ÷ 27 = 9.26 yd³

The calculator shows 9.26 cubic yards (and 250 cubic feet) for these inputs.

Why Depth Matters

Decomposed granite is a ground cover, not a structural base. The depth you choose depends on the application:

• 2 inches: Light foot traffic, decorative paths, or topping off an existing layer.
• 3 inches: Standard for most walkways and patios, providing a stable surface.
• 4 inches or more: For areas with vehicle traffic or if the DG is being used as a base for pavers.

Going deeper than 4 inches is rarely necessary for residential projects and can make the surface unstable or hard to walk on.

How to Measure Your Area

Most projects are not perfect rectangles. Here is how to handle common shapes:

• Rectangular: Measure length and width at the longest and widest points.
• Circular: Measure the diameter, divide by 2 to get the radius. Area = Ï€ × r².
• Irregular: Break the area into rectangles and triangles. Calculate each separately and add the volumes together.

For a triangle, the area is (base × height) / 2. Once you have the area in square feet, multiply by the depth (in feet) to get cubic feet, then divide by 27 for cubic yards.

Ordering and Waste Factor

DG is sold by the cubic yard, but you cannot order a fraction of a yard from most suppliers. You will need to round up to the nearest whole yard. Additionally, it is wise to add a waste factor of 10–15% to account for compaction, spillage, and uneven ground.

For the example above (9.26 yd³), you would order 10 cubic yards without waste. With a 10% waste factor, you need 10.19 yd³, so you would still order 11 yards. This ensures you have enough to complete the job without running short.

Common Mistakes

One frequent error is mixing units. If you measure length and width in feet, but depth in inches, you must convert the depth to feet before multiplying. Another mistake is forgetting that there are 27 cubic feet in a cubic yard, not 3. Finally, some people confuse cubic yards with square yards. Square yards measure area, not volume; you need depth to get volume.

Also, remember that DG compacts by about 10–20%. If you want a final depth of 3 inches, you may need to start with a slightly thicker layer (e.g., 3.5 inches) to account for settling. Most calculators, including this one, give the uncompacted volume, so order a bit extra.

Cost and Delivery Considerations

The calculator gives you volume, but not cost, because prices vary by region, supplier, and quality of DG. Typically, you will get a per-ton or per-cubic-yard price. To estimate cost, multiply the cubic yards by the price per yard. Delivery fees are often separate and may depend on the distance and quantity.

If you are buying in bags (usually 0.5 cubic feet each), divide the total cubic feet by 0.5 to get the number of bags. For the example, 250 ft³ would require 500 bags—this is rarely practical, so bulk delivery is usually better for large areas.

Frequently Asked Questions

How much decomposed granite do I need for a 10×10 area?

For a 10 ft by 10 ft area at 3 inches deep, the calculator gives 0.93 cubic yards. You would likely need to order 1 cubic yard, as most suppliers do not sell fractions.

What is the difference between decomposed granite and crushed stone?

Decomposed granite is a natural product that has weathered into small particles, often with a sandy texture. Crushed stone is mechanically crushed and has sharper edges. DG compacts well and is used for paths, while crushed stone is often used as a base under pavers.

How deep should decomposed granite be for a driveway?

For a driveway that will see regular vehicle traffic, a depth of 4 to 6 inches is recommended. The calculator can help you determine the volume for that depth, but you should also consider a base layer of larger crushed rock for stability.

Can I lay decomposed granite over grass?

It is not recommended. Grass will decompose and cause the DG to sink and become uneven. It is best to remove the grass and topsoil, then lay a weed barrier before adding DG.

How do I compact decomposed granite?

Spread the DG in layers of 2–3 inches, then use a plate compactor or a hand tamper. Lightly water the surface before compacting to help the particles bind together. Avoid compacting when it is too wet or too dry.

Does decomposed granite need a weed barrier?

Yes, a weed barrier fabric is recommended to prevent weeds from growing through the DG. It also helps keep the DG from mixing with the soil below, which reduces the need for replenishing.

Related

• Starting Line Ratio Calculator: Compare the Numbers
• Starting School Calculator QLD: Prep Age and Eligibility
• SR Zone GPA Calculator: How to Calculate Your GPA

in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1