Gravel calculator: how much gravel do I need

Enter the size of the area to see how much gravel, topsoil, turf or paving to order, using published supplier figures checked on 9 November 2026. Always confirm quantities with your supplier before you buy.

Your area

How do you want to enter the area?

Suggested: 30 to 50mm for decorative beds, 50mm for paths and driveways.

Gravel needed

Estimates from published supplier figures. Weights and bag sizes vary by product, so check with your supplier before ordering.

How the gravel calculation works

Every loose material starts with the same sum: area multiplied by depth gives a volume in cubic metres. Depth is entered in millimetres, so it is divided by 1,000 first. Gravel is sold by weight, so the volume is then multiplied by a density. Mainland Aggregates publishes 1.6 to 1.8 tonnes per cubic metre for gravel, and the calculator shows both ends of that range because the weight depends on the stone, its size and how wet it is.

A worked example: a path 5m long and 4m wide is 20 m². At 50mm deep that is 20 x 0.05 = 1 m³. At 1.6 to 1.8 tonnes per m³ the path needs 1.6 to 1.8 tonnes, which is two 850kg bulk bags at the lighter end and three at the heavier end. Ordering for the top of the range avoids running short halfway through.

Topsoil uses Rolawn's guide that one tonne of standard topsoil is roughly 0.67 m³. Turf is simpler because Rolawn rolls are about one square metre each, so the area in square metres plus an allowance for cutting gives the number of rolls. Paving divides the area by the space one slab takes up, including half the joint on each side.

What changes the result

Depth and what the area is for

Depth makes the biggest difference, because doubling it doubles the volume and the weight. Mainland Aggregates gives 30 to 50mm for decorative areas and 50mm for paths and driveways, with 100 to 150mm for drainage and sub-base layers under the top layer. Rolawn recommends 100 to 150mm of topsoil for turf or seed and 150 to 200mm for borders, with more for vegetables.

Type of material

Different stones and soils weigh different amounts for the same volume. Mainland Aggregates lists sand at 1.5 to 1.7 tonnes per m³ and MOT Type 1 sub-base at 1.9 to 2.1, so the gravel figures here should not be used for sub-base. Rolawn notes that topsoil bulk density varies with its type and make-up.

Bag size

Gravel bulk bags are normally sold by weight, around 850kg to 1 tonne, while Rolawn sells topsoil by volume, with a standard bulk bag of about 0.5 m³. The bag fields can be changed to match the supplier.

Slab size and joint width

Marshalls quotes many natural stone ranges laid with a 10mm joint, some porcelain with 5 to 8mm joints, and some ranges with actual sizes that exclude the joint. Wider joints mean slightly fewer slabs for the same area.

Common mistakes and tips

  • Mixing up millimetres and metres. 50mm is 0.05m. Entering 5 instead of 0.05 makes the order a hundred times too big.
  • Measuring an irregular shape as one rectangle. Rolawn suggests splitting odd shapes into smaller rectangles and adding them up, then rounding up.
  • Ordering exactly the calculated amount. Mainland Aggregates suggests rounding up to allow for compaction, spillage and levelling, and Rolawn recommends at least 5% extra turf.
  • Forgetting what sits underneath. A gravel drive or patio needs a sub-base, and a new lawn needs the topsoil ordered as well as the turf.
  • Leaving turf rolled up. Turf is a living product, so plan delivery for the day it will be laid.
  • Checking access. A bulk bag needs somewhere to be dropped, so make sure a lorry can reach a hard standing close to the work.

When to get a professional

Spreading decorative gravel or laying a small lawn is a manageable job for many homeowners. Driveways, patios on a slope, drainage problems and anything that needs a compacted sub-base are where a landscaper earns their fee, because a poor base leads to sinking slabs, puddles and gravel that spreads onto the lawn. A good landscaper will also measure the site and order the materials, which removes the risk of getting the quantities wrong.

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How this is worked out

  • Gravel: volume (m³) = area (m²) x depth (mm) / 1,000. Tonnes = volume x 1.6 to 1.8. Bulk bags = tonnes x 1,000 / bag weight in kg, rounded up.
  • Topsoil: volume (m³) = area x depth / 1,000. Tonnes = volume / 0.67. Bulk bags = volume / bag size in m³, rounded up.
  • Turf: rolls = area x (1 + extra % / 100), rounded up, with each roll about 1 m².
  • Paving: each slab covers (length + joint) x (width + joint). Slabs = area / that figure x (1 + extra % / 100), rounded up.

Related guides

Garden materials questions

How much gravel do I need for 10 square metres?

At 50mm deep, 10 m² needs 0.5 m³ of gravel. At the 1.6 to 1.8 tonnes per m³ published by Mainland Aggregates, that is 0.8 to 0.9 tonnes, so one 850kg bulk bag at the lighter end and two at the heavier end. At 30mm deep for a decorative bed the same area needs 0.3 m³, or 0.48 to 0.54 tonnes.

How deep should gravel be?

Mainland Aggregates gives 30 to 50mm for decorative garden areas and 50mm as the maximum for paths and driveways, with 100 to 150mm for drainage and sub-base layers. Deeper loose gravel on a path or drive is harder to walk and drive on, so a compacted sub-base under 50mm of gravel is the usual approach for a drive.

How many tonnes is a bulk bag of gravel?

Bulk bags are usually sold by weight, and Mainland Aggregates puts them at around 850kg to 1 tonne depending on the product. The calculator starts at 850kg and lets you change it to match the bag your supplier sells.

How much topsoil do I need for a new lawn?

Rolawn recommends 100 to 150mm of topsoil for turf or seed. At 150mm, 20 m² needs 3 m³, which is about 4.5 tonnes using Rolawn's guide of roughly 0.67 m³ per tonne, or six of Rolawn's 0.5 m³ bulk bags.

How many rolls of turf do I need?

Rolawn supplies rolls of about one square metre, so the number of rolls matches the area in square metres, plus at least 5% extra for cutting and shaping. A 20 m² lawn needs 21 rolls.

How many patio slabs do I need?

Divide the area by the space one slab takes up including its joint. A 600 x 600mm slab with a 10mm joint covers 0.61 x 0.61 = 0.3721 m², so 20 m² needs 53.75, rounded up to 54 slabs before any extra for cuts. Marshalls notes that some ranges quote sizes with the joint already included, so check the product sheet.

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