Gravel & Stone Calculator

Q: How much gravel do I need per square metre?

For a 50 mm depth of gravel (suitable for a decorative garden path), you need approximately 0.05 m3 per square metre, which equals around 75-85 kg or roughly one bulk bag per 14-20 m2. For a driveway sub-base using MOT Type 1 at 150 mm compacted depth, you need approximately 0.165 m3 per square metre loose (compaction factor of 1.3), which is around 345 kg per m2. Always account for compaction when ordering sub-base materials.

Q: What is the difference between MOT Type 1 and Type 3 sub-base?

MOT Type 1 is a crushed aggregate with graded particle sizes from 0 to 40 mm that compacts to a dense, stable sub-base. It is the standard material for driveways, paths and road construction in the UK and meets the Highways Agency Specification Series 800. MOT Type 3 is an open-graded unbound material used in sustainable drainage systems (SUDS) where water permeability is required. For standard driveways and hardstandings, specify MOT Type 1 at a minimum 150 mm compacted depth.

Q: How deep should gravel be for a driveway?

For a loose gravel driveway, use a minimum 50-75 mm depth of 20 mm angular chippings laid over a weed membrane and a compacted MOT Type 1 sub-base of at least 150 mm. For a bound resin or tarmac driveway, 100-150 mm of compacted MOT Type 1 sub-base is required beneath the surfacing. Under Building Regulations, driveways of 5 m2 or more must be permeable or drain to a suitable area - impermeable surfaces of this size require planning permission.

Q: How many bulk bags of gravel do I need?

A standard bulk bag (also called a dumpy bag or tonne bag) holds approximately 0.6-0.8 m3 of gravel or stone, depending on the material and how it is loaded. For decorative stone or pea gravel at 1.6 t/m3 density, one bulk bag weighs around 800-900 kg. To calculate the number of bags needed, divide your required volume by 0.7 m3 (a typical average bulk bag volume) and round up. Our calculator above gives you the exact bag count for your chosen material.

Q: What size gravel should I use for a path or driveway?

For garden paths, 10 mm or 14 mm pea gravel or golden gravel is comfortable underfoot and less likely to be kicked out than larger sizes. For driveways, 20 mm angular chippings (such as limestone or granite) bind better than round pea gravel and are less likely to scatter. Angular chippings self-lock under traffic pressure. Pea gravel and round stones are better suited to decorative borders and features than trafficked areas.

Q: What waste allowance should I use for gravel and stone?

Add 10% to your calculated quantity for a straightforward rectangular area. For areas with many curves, borders or irregular edges, use 15%. For MOT sub-base, increase your calculated loose volume by 30% (compaction factor of 1.3) before ordering - the material reduces significantly in volume when compacted. It is generally better to order slightly more than needed, as matching materials in a second order can be difficult.

How much gravel or stone do I need?

Multiply the area by the depth to get the volume, then multiply by the bulk density of the material to convert to tonnes. Pea gravel and decorative chippings typically weigh around 1.5-1.7 t/m³, while MOT Type 1 sub-base compacts to around 2.1 t/m³ when laid. Our calculator covers the most common gravel and stone types used in UK groundworks and landscaping, including MOT sub-base, decorative chippings, sharp sand, and topsoil - with bulk bag and loose tonne quantities, compaction factors, and full cost estimates. For paths and driveways, UK guidance suggests a minimum 100 mm depth of compacted sub-base beneath a bound surface.

Volume, weight, and bag/tonne quantities for any aggregate. Supports MOT sub-base, decorative gravel, sharp sand, ballast, and more.

Material

Density: -

Density (t/m²) - override if known

Overage / Waste (%) 10% recommended for paths and driveways to allow for compaction and spillage.

Compaction factor (%) MOT Type 1: add 15-20%. Gravel/decorative: 0% (loose, no compaction). Sharp sand: 10%.

Delivery format

Areas

Enter length x width for rectangular areas, or enter area (m²) directly and leave length/width blank.

Name / description Length (m) Width (m) Depth (mm)

For circular areas use: length = diameter, width = diameter x 0.785 (π/4).

Or enter total area directly (m²) - overrides area grid above

Depth (mm)

Job Costing (optional)

Material cost per tonne

Delivery (flat fee)

Labour cost

Rate x total area

UK Market PricesFills in the material cost fields with current UK market prices. You can review and edit each price before applying.

Results

Total Area
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m²

Volume (inc. waste)
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m²

Weight (inc. waste)

tonnes

Bulk bags

to order

Area Breakdown

Area	Dimensions	Area (m²)	Depth	Net vol (m²)	With waste (m²)	Weight (t)

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Frequently Asked Questions

How much gravel do I need per square metre?

At 50 mm depth (garden path): approximately 75-85 kg per m² - one bulk bag covers around 14-20 m². For a driveway MOT sub-base at 150 mm compacted: approximately 345 kg per m² loose (add 30% for compaction). Always account for compaction when ordering sub-base materials.

What is the difference between MOT Type 1 and Type 3 sub-base?

MOT Type 1 is a dense-graded 0-40 mm crushed aggregate that compacts to a stable, load-bearing sub-base - the standard for driveways and paths in the UK. MOT Type 3 is open-graded and permeable, used in sustainable drainage (SUDS) systems. For standard driveways, specify MOT Type 1 at minimum 150 mm compacted depth.

How deep should gravel be for a driveway?

Loose gravel driveways: minimum 50-75 mm of 20 mm angular chippings over weed membrane and at least 150 mm compacted MOT Type 1 sub-base. Bound (resin/tarmac) driveways: 100-150 mm compacted sub-base. Note: driveways over 5 m² must be permeable or drain to a suitable area under Building Regulations - impermeable surfaces of this size require planning permission.

How many bulk bags of gravel do I need?

A standard bulk bag (dumpy bag) holds approximately 0.6-0.8 m³ of gravel or stone. For decorative stone at ~1.6 t/m³, one bulk bag weighs around 800-900 kg. Divide your required volume by 0.7 m³ and round up for a bag count estimate. The calculator above gives you the exact quantity for your chosen material.

What size gravel should I use for a path or driveway?

For garden paths: 10 mm or 14 mm pea gravel - comfortable underfoot and less likely to scatter than larger sizes. For driveways: 20 mm angular chippings (limestone or granite) self-lock under traffic and bind better than round pea gravel. Round stones scatter easily and are better for decorative borders than trafficked areas.

What waste allowance should I use for gravel and stone?

Add 10% waste for straightforward rectangular areas; 15% for irregular shapes with curves or borders. For MOT sub-base, increase your calculated volume by 30% for compaction before ordering. It is generally better to order slightly more - matching materials in a second order can be difficult.

Material Densities

Material	Density

Typical Depths

Decorative gravel / pea gravel: 40-50 mm (paths/borders), 50-75 mm (driveways)
MOT Type 1 sub-base: 100-150 mm compacted (domestic drives), 200 mm (commercial)
Decorative slate / chippings: 30-50 mm
Sharp sand (screeding bed): 30-50 mm
Sharp sand (concrete blinding): 50-75 mm
Topsoil (new lawn): 100-150 mm
Topsoil (borders): 150-300 mm
Ballast (concrete sub-base): 100-150 mm

Tips

Always allow 10-15% extra for uneven ground, compaction, and wastage
MOT Type 1 compacts by up to 20% - order uncompacted volume, not finished depth
Bulk bags (800 kg - 1 t) suit small/medium jobs. Loose loads suit anything over 2-3 t
A standard tipper lorry carries 15-20 t; a grab lorry suits awkward access
Use a membrane / weed fabric under decorative gravel to suppress weeds
For driveways, SuDS regulations may require a permeable surface - gravel qualifies

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