Project guide

How much artificial grass do I need, and what goes under it?

To work out how much artificial grass you need, decide which way the rolls will run, count the strips of 2m or 4m wide grass, and add a little length for trimming. The base underneath matters as much as the grass.

Updated 14 October 2026 Based on manufacturer guidance, sources below

The short answer

Rolls are usually 2m or 4m wide and cut to length. Strips = lawn width / roll width, rounded up; each strip = lawn length + about 100mm for trimming. Underneath, the HTA guidance is 75 to 100mm of compacted MOT Type 1 and 15 to 20mm of granite (grano) dust. A 6 x 5m lawn in 4m rolls needs 2 pieces 5.1m long (40.8 m²), about 6.9 tonnes of MOT Type 1 (9 bulk bags) and 1.1 tonnes of granite dust.

The formula

Strips = width / roll width, rounded up (try both directions and use the one with less waste)
Each strip = length + 0.1m for trimming; grass to order = strips x roll width x strip length
MOT Type 1 (tonnes) = area x 0.1 x 2.1 x 1.1, in 800kg bulk bags
Granite dust (tonnes) = area x 0.02 x about 1.7 x 1.1
Joining tape = (strips - 1) x strip length, plus 10%

Worked example

A 6 x 5m lawn (30 m²) with 4m wide grass:

Run the rolls across the 5m side: 6 / 4 = 1.5, so 2 strips 5.1m long, 40.8 m² of grass
The other way would need 2 strips 6.1m long (48.8 m²), so this is the cheaper layout
MOT Type 1: 30 x 0.1 x 2.1 x 1.1 = 6.9 tonnes
Granite dust: 30 x 0.02 x 1.7 x 1.1 = 1.1 tonnes
Joining tape: 6m for the one 5.1m seam

Work it out for your job

Change the measurements and the quantities update straight away.

Lawn length (m)

Lawn width (m)

Roll width

MOT Type 1 depth

Lawn area: 30 m²
Grass to order: 40.8 m² (2 x 4m wide)
Sub-base: 6.9 tonnes MOT Type 1 + 1.1 tonnes granite dust

Your list

2Pieces of grass 4m wide x 5.10m long
9MOT Type 1, 800kg bulk bags (100mm, for estimating)
1.1tonnes of granite dust (20mm laying course)
1Weed-control fabric, 2 x 25m rolls
6metres of joining tape and adhesive

Lay every piece with the pile facing the same way, or the joins will show.

Price the sub-base

Opens SmartBuild with the MOT Type 1 and weed-control fabric added, priced from supplier product feeds. SmartBuild does not price artificial grass or granite dust yet.

Materials checklist

Artificial grassUsually 2m or 4m wide, cut to length. 2m and 4m widths from the same range colour-match; 5m widths may not.
MOT Type 1Crushed stone sub-base, laid in two layers and compacted to 75 to 85mm.
Granite (grano) dustThe 15 to 20mm laying course, 6mm to dust, compacted smooth. No more than 25mm.
Weed membraneGeotextile under the base and, on some installs, under the grass.
Joining tape and adhesiveFor seams between strips.
Edging and fixingsTreated timber or composite edging, with galvanised nails or staples to fix the grass.

You'll also need

Turf cutter or spade
Plate compactor (hire)
Sharp carpet knife and spare blades
Stiff brush or power brush
Rake and spirit level

Step by step

Clear and digRemove the turf and dig out 75 to 100mm below the finished level.
Fit the edgingFix the edging around the perimeter so it holds the base and gives you something to fix the grass to.
Lay the sub-baseLay MOT Type 1 in two 40 to 50mm layers, compacting each one.
Add the laying courseSpread 15 to 20mm of granite dust, level it and compact it.
Lay, join and brushRoll out the grass with the pile all one way, join seams with tape and adhesive, fix the edges and brush the pile up.

Tips from the manufacturers

Keep the pile direction the same on every strip, or the joins will show.
Mixing a 4m and a 2m strip can cut waste on awkward widths; the HTA notes you lose about 100mm at each join to trimming.
Unroll the grass and leave it in the sun for a couple of hours so the creases drop out before cutting.
For dogs or poorly drained ground, the HTA describes a deeper, more open MOT Type 3 base instead.

Mistakes to avoid

Laying straight onto soil or old turf, so the lawn goes lumpy.
Using sharp sand alone as the laying course, which can wash out and rut.
Ordering the exact lawn size with nothing for trimming.
Running strips in different directions.

Frequently asked questions

What widths does artificial grass come in?

Usually 2m and 4m, and some ranges also come in 5m. It is cut to the length you order.

How much MOT Type 1 do I need for artificial grass?

The HTA recommends allowing 100mm for estimating, compacted to 75 to 85mm. That is about 0.23 tonnes per m², or 6.9 tonnes for 30 m² including 10%.

How much granite dust under artificial grass?

15 to 20mm, and no more than 25mm, over the compacted MOT Type 1. About 1.1 tonnes for 30 m².

Can I lay artificial grass on soil?

It is not recommended. Without a compacted stone base the surface sinks and goes lumpy, and weeds come through.

How much extra artificial grass should I order?

Allow about 100mm on the length of each strip for trimming, and plan the layout so strips run the direction that wastes least.

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 much decking do I need?Boards are the easy part. The frame underneath is where most DIY lists go wrong, so this guide follows the Timber Decking & Cladding Association (TDCA) handbook.

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