Decomposed Granite Calculator: Square Feet & Depth

This decomposed granite calculator works out the volume of decomposed granite you need to cover a given square footage at a chosen depth. You enter the length and width of the area in feet (or meters) and the desired depth in inches (or centimeters), and the calculator returns the volume in cubic yards and cubic feet. This is the number you need to order from a landscape supplier.

Formula

The formula for calculating decomposed granite volume is straightforward:

Volume (cubic feet) = Length (ft) × Width (ft) × Depth (in) ÷ 12

Volume (cubic yards) = Length (ft) × Width (ft) × Depth (in) ÷ 324

Where:

• Length is the longest dimension of the area in feet (or meters, converted to feet).
• Width is the shorter dimension in feet.
• Depth is how thick you want the decomposed granite layer in inches.

The divisor 12 converts inches to feet (since there are 12 inches in a foot). The divisor 324 comes from converting cubic feet to cubic yards: 1 cubic yard = 27 cubic feet, and 27 × 12 = 324.

Worked Example

Using the default values from the calculator above (length = 40 ft, width = 25 ft, depth = 3 in):

1. Calculate the area: 40 ft × 25 ft = 1,000 square feet.
2. Convert depth to feet: 3 in ÷ 12 = 0.25 ft.
3. Volume in cubic feet: 1,000 sq ft × 0.25 ft = 250 cubic feet.
4. Volume in cubic yards: 250 cubic feet ÷ 27 = 9.26 cubic yards (rounded to two decimals).

The calculator gives the same result: 9.26 yd³ and 250 ft³.

Why Depth Matters

Decomposed granite (DG) is a popular, affordable material for paths, patios, and driveways. Unlike a solid slab, DG is a loose aggregate that compacts over time. The depth you need depends on the application:

• Walkways and light foot traffic: 2–3 inches of compacted DG is usually enough.
• Patios and seating areas: 3–4 inches provides a more stable base.
• Driveways (vehicular traffic): 4–6 inches, often over a geotextile fabric and a base layer of larger crushed rock.

If you apply DG too thinly (under 2 inches), it will shift, rut, and need frequent replenishing. If you apply it too thickly, you waste money and may create an unstable, spongy surface.

How to Measure Your Area

For a simple rectangle, measure length and width in feet. For irregular shapes, break the area into smaller rectangles, triangles, or circles, calculate each, and add them together. For a circle, measure the diameter (the distance across the center) and use the formula: Area = π × (diameter/2)². For a triangle, multiply the base by the height and divide by 2.

If you are working in meters, convert to feet before using the calculator (1 meter = 3.28084 feet). Or use the calculator with meters for length/width and centimeters for depth, but note that the output will be in cubic meters, not cubic yards. The calculator above expects feet and inches, so stick to those units for the default setup.

Ordering Decomposed Granite

Decomposed granite is sold by the cubic yard (loose bulk) or by the bag (typically 0.5 cubic feet per bag). Once you have the volume in cubic yards, multiply by 27 to get cubic feet. If you buy bags, divide the total cubic feet by the bag size to get the number of bags, and round up to the nearest whole bag.

For bulk orders, suppliers usually deliver by the cubic yard. It is wise to order about 10% extra to account for compaction (DG settles about 10% when compacted) and for uneven ground. For example, if your calculated volume is 9.26 cubic yards, order about 10.2 cubic yards.

Common Mistakes

• Mixing units: Always use the same unit system. If you measure length in feet, use inches for depth, not centimeters.
• Forgetting compaction: DG compacts down, so if you need a final depth of 3 inches, you may need to start with 3.5 inches of loose material.
• Ignoring slopes: On a slope, you may need more DG at the bottom to create a level surface. Measure the slope’s run and rise to calculate extra volume.
• Rounding too early: Do not round intermediate numbers. Only round the final volume to the nearest cubic yard (or bag).

Cost Considerations

The price of decomposed granite varies by region, color, and whether it is screened (sifted to remove fines) or unscreened. Generally, bulk DG costs less per cubic yard than bagged DG. You may also need to budget for delivery fees, which can be significant for large orders. To get an accurate cost, contact local landscape suppliers for current quotes. The calculator gives you the volume, so you can compare prices per cubic yard.

Frequently Asked Questions

How many square feet does a cubic yard of decomposed granite cover?

It depends on depth. At 3 inches deep, one cubic yard covers 108 square feet (since 27 cubic feet ÷ 0.25 ft = 108 sq ft). At 2 inches deep, it covers 162 square feet. At 4 inches deep, it covers 81 square feet. Use the formula: coverage (sq ft) = 27 ÷ (depth in inches / 12).

Do I need to compact decomposed granite?

Yes, compaction is essential for a stable surface. After spreading DG, use a plate compactor (for larger areas) or a hand tamper (for small paths) to compact it. This reduces settling and helps the DG interlock. If you skip compaction, the surface will be loose and easily displaced.

What is the difference between decomposed granite and crushed stone?

Decomposed granite is naturally weathered granite that has broken down into small particles, including fines (sand and clay-like material). Crushed stone is mechanically crushed rock, often with sharper edges and no fines. DG compacts into a firm, almost solid surface, while crushed stone stays more permeable and is often used as a base layer.

Can I use decomposed granite over grass?

It is not recommended. Grass and weeds will push through the DG, and the DG will not compact well over organic material. For a lasting path or patio, remove the grass and topsoil, lay a weed barrier (geotextile fabric), and then install a base layer of crushed rock before adding DG.

How long does decomposed granite last?

With proper installation and compaction, a DG path can last many years. However, it will need occasional replenishing, especially in high-traffic areas or after heavy rain. Adding a stabilizer (a liquid binder) can extend the life and reduce maintenance, but it adds cost.

Is decomposed granite safe for drainage?

Yes, DG is permeable, meaning water drains through it. This makes it a good choice for areas where you want to reduce runoff. However, on slopes, heavy rain can wash DG away. Installing edging or using a stabilizer can help prevent erosion.

Related

• Area of a Circle Calculator in Square Feet
• Area Calculator for Feet and Inches
• Area Calculator UK: Measure Square Metres and Feet

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