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Project guide

How much gravel and sub-base do I need for a driveway?

A gravel driveway is two layers: a compacted sub-base that carries the weight of the car, and a thin layer of gravel on top. Work out the area, then the tonnes of each layer, and order in bulk bags.

Updated Based on manufacturer guidance, sources below

The short answer

For cars, lay 150mm of compacted MOT Type 1 sub-base (about 2.1 tonnes per m³) on a separating fabric, topped with 50mm of 20mm gravel (about 1.6 tonnes per m³). A 6 x 3m driveway needs about 6.2 tonnes of sub-base (8 bulk bags) and 1.6 tonnes of gravel (2 bulk bags), including 10% extra.

The formula

  • Area (m²) = length x width
  • MOT Type 1 (tonnes) = area x 0.15 x 2.1, plus 10% (use 0.1 for a footpath)
  • Gravel (tonnes) = area x 0.05 x 1.6, plus 10%
  • Bulk bags = tonnes / 0.8; fabric = area + 10%, in 50 m² rolls

Worked example

A 6 x 3m driveway for a car:

  • Area: 6 x 3 = 18 m²
  • Sub-base: 18 x 0.15 x 2.1 x 1.1 = 6.2 tonnes, so 8 bulk bags
  • Gravel: 18 x 0.05 x 1.6 x 1.1 = 1.6 tonnes, so 2 bulk bags
  • Fabric: 19.8 m², so 1 roll
  • Digging out: 18 x 0.2 = 3.6 m³ of soil, more once it is loosened

Work it out for your job

Change the measurements and the quantities update straight away.

Driveway area
18 m²
MOT Type 1 (150mm)
about 6.2 tonnes
Gravel (50mm)
about 1.6 tonnes
Soil to dig out
about 3.6 m³

Your list

  • 1Separating fabric, 2 x 25m rolls
  • 8MOT Type 1 sub-base, 800kg bulk bags
  • 220mm gravel, 800kg bulk bags
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Materials checklist

  • MOT Type 1 sub-baseCrushed stone that compacts into a firm, free-draining base. Sold in bulk bags of about 800kg or loose by the tonne.
  • 20mm gravelAngular gravel locks together better under tyres than rounded pea shingle.
  • Separating fabricA permeable geotextile under the sub-base stops it mixing into the soil.
  • EdgingTimber, steel or concrete kerbs keep the sub-base and gravel in place.
  • Gravel stabilising grids (optional)Honeycomb panels that reduce rutting and scatter, especially on slopes.

You'll also need

  • Plate compactor (hire)
  • Skip or grab lorry for the dug-out soil
  • Spade, shovel, rake and wheelbarrow
  • String line and pegs to set the levels and a fall for drainage

Step by step

  1. Measure and check permissionMeasure the length and width. A new or replaced front driveway over 5 m² must be permeable or drain to a lawn or border, or it needs planning permission.
  2. Dig outExcavate to about 200mm below the finished level for a car driveway: 150mm sub-base plus 50mm gravel.
  3. Lay fabric and edgingLay the separating fabric with overlapping joints and fix the edging to the finished height.
  4. Lay and compact the sub-baseSpread MOT Type 1 in layers of no more than about 75mm and compact each one with a plate compactor.
  5. Spread the gravelSpread the gravel to about 50mm and rake it level. Any deeper and tyres and feet sink in.

Tips from the manufacturers

  • Loose gravel on a permeable sub-base usually counts as a permeable surface for planning purposes.
  • Keep the gravel to about 50mm. A thicker layer feels loose and is hard to drive and walk on.
  • Order the sub-base and gravel together where you can, to save on delivery, and have the bags dropped as close to the drive as possible.
  • Use 100mm of sub-base only for paths and areas that will never take a car.

Mistakes to avoid

  • Laying gravel straight onto soil with no sub-base, which ruts and sinks within months.
  • Compacting the sub-base in one thick layer, which leaves the bottom loose.
  • Leaving out edging, so gravel spreads onto the pavement and lawn.
  • Forgetting the cost and space for the dug-out soil.

Frequently asked questions

How deep should a gravel driveway be?

About 200mm in total for cars: 150mm of compacted MOT Type 1 sub-base and 50mm of gravel on top.

How much gravel do I need for a driveway?

At 50mm deep, allow about 0.09 tonnes of 20mm gravel per m² including 10%. An 18 m² driveway needs about 1.6 tonnes, which is two 800kg bulk bags.

What size gravel is best for a driveway?

20mm angular gravel is the usual choice. It locks together and does not stick in tyre treads as much as smaller stone.

Do I need planning permission for a gravel driveway?

Not usually for a permeable surface. A new or replaced front driveway over 5 m² needs planning permission only if it is not permeable and does not drain to a lawn or border.

Sources

Quantities are estimates for typical jobs, using the coverage figures above. Products vary, so check the data sheet for the product you buy, and talk to a professional for structural, electrical or gas work. SmartBuild is independent and not affiliated with any of the manufacturers listed.

How much gravel do I need? Tonnes and bagsTo work out how much gravel you need, multiply the area by the depth to get cubic metres, then by the weight of a cubic metre of your gravel to get tonnes. How many paving slabs do I need, and how much sub-base?To work out how many paving slabs you need, divide the patio area by the area of one slab and add 10% for cuts. The sub-base, mortar bed and jointing follow from the same area. How many bricks do I need for a wall?To work out how many bricks you need, measure the face of the wall, multiply by the number of bricks per square metre for the wall thickness and add a little for cuts and breakages. Then work out the mortar to lay them.

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