Granite Dust Calculator UK: Volume & Coverage

This calculator works out how much granite dust (also called granite screenings or granite fines) you need for a project in the UK, based on the length and width of the area and the depth of the layer you want. You enter the area dimensions in feet and the depth in inches, and you get the volume in cubic yards and cubic feet, which you can then convert to tonnes using the density of granite dust. The result is a volume, not a weight, because the density of granite dust varies by supplier and moisture content.

Formula

The calculator uses the standard volume formula for a rectangular prism: Volume = Length × Width × Depth. Since the inputs are in feet and inches, the formula converts the depth from inches to feet by dividing by 12, then divides by 27 to get cubic yards (because there are 27 cubic feet in a cubic yard).

In symbols: V (yd³) = (L × W × D) / 324, where L is the length in feet, W is the width in feet, and D is the depth in inches. The 324 comes from 12 inches per foot × 27 cubic feet per cubic yard. The second output, cubic feet, is simply L × W × D / 12.

Worked Example

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

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Calculate volume in cubic feet: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.259 yd³ (rounded to 9.26 yd³)

The calculator shows 9.26 yd³ and 250 ft³, which matches the manual calculation.

What Is Granite Dust and What Is It Used For?

Granite dust is a fine aggregate produced when granite is crushed and screened. The particles range from dust to about 5 mm, and it compacts well, making it a popular base material for patios, paths, driveways, and as a bedding layer for paving slabs. In the UK, it is often sold as “granite screenings� or “granite chippings� and is used by landscapers and DIYers for:

• Laying paving slabs – a 25–50 mm bed of granite dust provides a stable, level base.
• Path and patio sub-base – compacted granite dust creates a firm surface that resists weeds.
• Filling gaps between pavers – as a jointing material when mixed with a little cement.
• Under artificial grass – a 10–20 mm layer helps with drainage and smoothing.

Granite dust is often chosen over sharp sand because it locks together better and doesn’t wash out as easily.

How to Use the Calculator

Measure the length and width of the area in feet using a tape measure. For irregular shapes, break the area into rectangles, calculate each one separately, and add the volumes together. Decide on the depth – for a footpath, 50 mm (about 2 inches) is common; for a driveway, 100 mm (about 4 inches) or more may be needed. Enter the values and the calculator gives the volume in cubic yards and cubic feet.

To convert volume to weight (tonnes), multiply the cubic yards by the density of granite dust. A typical density is around 1.5 tonnes per cubic yard (about 1.8 tonnes per cubic metre), but it varies. Check with your supplier for the exact figure, as moisture can increase weight significantly.

Common Mistakes and How to Avoid Them

• Mixing units: Always measure in feet for length and width, and inches for depth. If you measure in metres, convert to feet first (1 m = 3.28084 ft).
• Forgetting compaction: Granite dust compacts by about 10–15%. If you need a 3-inch compacted layer, you may need to order 10–15% more to allow for compaction. The calculator gives the loose volume, so add extra if you are compacting.
• Rounding too early: If you round the volume to 1 decimal place before ordering, you might under-order. Buy slightly more than the calculated amount, as it’s hard to match an exact colour if you need a top-up later.
• Assuming all granite dust is the same: Density varies by source and particle size. Some suppliers sell by weight, some by volume. Always confirm the density with the supplier.

Granite Dust vs. Other Aggregates

Granite dust is often compared to sharp sand, limestone dust, and MOT Type 1. Here’s a quick comparison:

• Granite dust: Fine, compacts well, good drainage, but can be dusty when dry. Ideal for bedding and jointing.
• Sharp sand: Coarser, less binding, cheaper, but washes out more easily. Good for mortar.
• Limestone dust: Similar to granite dust but may be more alkaline, which can affect plants. Not ideal for paths near acid-loving plants.
• MOT Type 1: A graded aggregate with larger stones, used as a sub-base for driveways. Not a substitute for granite dust as a bedding layer.

For a decorative path, granite dust is often preferred because it stays in place and looks natural. For a driveway that will bear heavy vehicles, a compacted sub-base of MOT Type 1 is usually required, with granite dust as a finishing layer.

Cost and Ordering Considerations

Granite dust is sold in bulk bags (typically 800 kg to 1 tonne) or by the tonne. The cost varies by region and supplier, but you can estimate by converting your volume to tonnes. Using the example above, 9.26 yd³ × 1.5 tonnes/yd³ = 13.89 tonnes. That would be about 14 bulk bags, though you should always confirm the bag weight with the supplier.

When ordering, consider the following:

• Delivery charges – often free over a certain quantity, but check.
• Minimum order – some suppliers only deliver full loads.
• Storage – bulk bags need a dry, level area; granite dust can harden if left wet.
• Waste – order 10% extra to cover spillage and compaction losses.

It’s also worth asking if the supplier can deliver in smaller bags if you only need a small amount.

Safety and Handling

Granite dust is a fine material that can create dust when dry. Wear a dust mask when handling it, especially if you are mixing it dry. Avoid inhaling the dust, as it can irritate the lungs. When laying, keep the area damp to reduce dust. If you are using it as a jointing material mixed with cement, wear gloves and eye protection. Granite dust is not hazardous, but it is heavy – use proper lifting techniques when moving bags.

For children’s play areas, granite dust is sometimes used as a surface, but it must be laid to the correct depth (usually 150 mm) to meet safety standards. Check with a professional if you are using it for this purpose.

Frequently Asked Questions

How many tonnes of granite dust do I need?

Multiply the volume in cubic yards by the density (typically 1.5 tonnes per cubic yard). For the example, 9.26 yd³ × 1.5 = 13.89 tonnes. Always confirm the density with your supplier, as it can range from 1.4 to 1.6 tonnes per cubic yard.

Can I use granite dust instead of sharp sand for paving?

Yes, granite dust is often used as a bedding layer for paving slabs. It compacts well and provides a stable base. However, it is finer than sharp sand, so it may not be suitable for mortar mixes that require coarser sand.

What depth of granite dust do I need for a path?

For a pedestrian path, a compacted depth of 50 mm (about 2 inches) is typical. For a driveway, you may need 100 mm or more, depending on the sub-base. Always check with a landscaper for heavy-use areas.

Does granite dust compact?

Yes, granite dust compacts well, but it will reduce in volume by about 10–15%. When ordering, add extra to account for compaction. For a 50 mm compacted layer, order about 55–60 mm of loose material.

Is granite dust the same as decomposed granite?

Not exactly. Decomposed granite is a natural product that has weathered over time, while granite dust is a by-product of crushing. Both are used for similar purposes, but decomposed granite may have a more varied particle size and is often more expensive.

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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