Decomposed Granite per Square Foot: How Much You Need

To calculate how much decomposed granite you need per square foot, multiply the area’s length by its width to get square footage, then multiply that by the desired depth in inches and divide by 12 to get cubic feet, or divide by 324 to get cubic yards. For a typical 3-inch depth, you’ll need about 0.25 cubic feet (0.0093 cubic yards) of decomposed granite per square foot. This article explains the formula, how to measure your space, and factors that affect your final amount.

Formula

The volume of decomposed granite needed is calculated using the basic volume formula for a rectangular prism:

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

To convert to cubic yards (the common purchase unit for bulk material):

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

Variables:

• Length (L): the longest side of the area in feet.
• Width (W): the shortest side of the area in feet.
• Depth (D): the desired thickness of the decomposed granite layer in inches.
• 324: conversion factor (1 cubic yard = 27 cubic feet; 27 × 12 = 324).

Worked Example

Using the default values from the calculator (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. Calculate volume in cubic feet: 1,000 sq ft × 0.25 ft = 250 cubic feet.
4. Convert to cubic yards: 250 ft³ ÷ 27 = 9.26 cubic yards.

The calculator gives the same result: 9.26 yd³ (or 250 ft³). This matches the formula exactly.

Why Depth Matters Most

The depth of the decomposed granite layer is the single biggest factor in how much you need. A common mistake is to underestimate depth, leading to a thin layer that washes away or fails to suppress weeds. Here are typical depth guidelines:

• 2 inches: light foot traffic areas, temporary paths, or as a base under pavers.
• 3 inches: standard for most walkways and patios, providing good stability.
• 4 inches: recommended for driveways or areas with heavier traffic, as it resists rutting.

Remember that decomposed granite compacts down by about 10–15% after installation. If you want a final depth of 3 inches, you should order about 3.3–3.5 inches worth of material to account for compaction.

How to Measure Your Area

Accurate measurement is essential for ordering the right amount. Here’s a step-by-step approach:

1. Break the area into rectangles: For L-shaped or irregular spaces, divide into smaller rectangles, calculate each, then add them together.
2. Measure length and width: Use a tape measure for small areas or a measuring wheel for large ones. Round up to the nearest foot.
3. For circular areas: Measure the diameter (distance across the center), divide by 2 to get the radius, then use the formula: area = π × radius².
4. For triangular areas: Multiply the base by the height, then divide by 2.
5. Add 5–10% extra: This accounts for compaction, uneven ground, and spillage during installation.

Common Mistakes and How to Avoid Them

Even with the right formula, people often make errors that lead to ordering too much or too little. Watch out for these:

• Mixing units: Always convert depth to feet before multiplying. Using inches directly in the volume formula gives a number that is 12 times too large.
• Forgetting compaction: As noted, decomposed granite settles. Ordering exactly the calculated volume will leave you short.
• Ignoring the sub-base: If you’re installing over soft soil, you may need a layer of larger crushed rock (e.g., ¾-inch) beneath the decomposed granite. This adds to the total volume of material you need.
• Rounding too early: When doing manual calculations, keep at least two decimal places until the final answer, then round up to the nearest half-yard.

Comparing Bulk vs. Bagged Purchase

Decomposed granite is sold either in bulk by the cubic yard or in bags (typically 0.5 cubic feet or 50 pounds). Here’s how to decide:

• Bulk (by the yard): Best for areas larger than 100 square feet. It’s cheaper per cubic foot and delivered in a truck, but you’ll need a place to dump it and a wheelbarrow to spread it.
• Bags: Easier to transport and handle, ideal for small patches or if you don’t have a vehicle that can haul bulk. However, the cost per cubic foot is significantly higher.

To convert from cubic feet to bags: divide the total cubic feet by the bag size (e.g., 250 ft³ ÷ 0.5 ft³ = 500 bags). Always round up to the nearest whole bag.

Cost Considerations

While prices vary by region and supplier, you can estimate the cost by multiplying the total cubic yards by the price per yard (bulk) or by the number of bags times the price per bag. A typical 3-inch layer over 1,000 square feet requires about 9.3 cubic yards. If you’re quoted a price per ton, remember that decomposed granite weighs roughly 1.4 tons per cubic yard (varies by moisture and rock type). Always call local suppliers for current pricing and delivery fees, as these can significantly affect the total.

Frequently Asked Questions

How many square feet does a ton of decomposed granite cover?

At a 3-inch depth, a ton of decomposed granite (about 0.7 cubic yards) covers roughly 75–80 square feet. At 2 inches, it covers about 110–120 square feet. The exact coverage depends on the material’s density and moisture content.

Can I use decomposed granite for a driveway?

Yes, but it needs a thicker layer (4–5 inches) and a proper base of larger crushed rock. For regular car traffic, consider mixing decomposed granite with a stabilizer or using a product specifically designed for driveways, as plain DG can rut under heavy loads.

How do I keep decomposed granite from washing away?

Proper edging (metal or plastic borders) helps contain it. Also, a layer of landscape fabric underneath prevents weeds and helps with drainage. For slopes, use a stabilizer or install a French drain to divert water.

Do I need to wet and compact decomposed granite?

Yes. After spreading, moisten the DG lightly (not soaking) and compact it with a plate compactor or hand tamper. This locks the particles together and creates a firm, stable surface. Repeat the process in layers if installing more than 3 inches.

Is decomposed granite safe for pets?

Generally yes. It’s a natural material, but the fine dust can be irritating to some animals’ respiratory systems. Also, the sharp edges of the particles can be rough on paws. Rinsing the area after installation can reduce dust. If you have concerns, consult your veterinarian.

Can I lay decomposed granite over grass?

It’s not recommended. Grass will decompose underneath, causing the surface to sink and become uneven. Remove the grass and topsoil (at least 2–3 inches) before installing DG to ensure a stable base.

Related

• Acre Foot to Gallons Calculator
• Acre ft to Gallons Calculator: How to Convert
• Lawn Acreage Calculator: Feet to Acres

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