Turf Calculator

Key Takeaways

• A roll of turf covers 1m² and measures about 1.7m x 0.6m, so the number of rolls equals the lawn area in square metres plus the extra for cuts.
• Turf for a straight-sided lawn needs about 5% extra for cuts and shaping, and a lawn with curves, beds or awkward corners needs 10% to 15% extra.
• A new lawn on bare or poor ground needs 150mm of topsoil under the turf, while good existing topsoil only needs a 25mm layer raked over it.
• New topsoil settles once it is down, so an order needs about 15% on top of the area times the depth to finish at the right level.
• Topsoil for a 5m x 4m new lawn comes to about 3,450L at 150mm with 15% for settlement, which is five 700L builders bags.

Turf is the bit everyone measures carefully. The soil underneath is the bit everyone guesses, and it is the soil that decides whether the lawn looks good in two years. So this calculator does both jobs. It counts the rolls, adds the extra for cuts, and works out the soil in litres against the bags we actually sell, with the settlement allowance built in.

How Do I Calculate How Much Turf I Need?

Turf is worked out from the lawn area in square metres, because one roll covers 1m². Multiply the length by the width, add 5% for cuts, and round up to the next whole roll. A 5m x 4m lawn is 20m². Add 5% and you get 21m², so 21 rolls. That is the whole sum for a rectangle. The extra is there because turf gets cut. Every edge against a path, every curve round a bed and every corner round a shed costs you a strip. Here is how I picked the allowance:

Turf is a living product, so running short is worse than having a few rolls over. A second delivery costs more than the spare rolls do, and the second batch can look a shade different from the first.

How to Measure Your Lawn for Turf

Measure the lawn as the finished shape, after the beds and paths are marked out. Take every measurement in the same unit, and measure twice.

1. For a rectangle, measure the length and the width at the widest points.
2. For an L shape, split it into two rectangles and measure each one. Do not count the corner twice.
3. For a circle, measure straight across the middle, edge to edge. The calculator does the rest.
4. For a triangle, measure one side as the base, then the height from that side straight across to the opposite corner.
5. For a really odd shape, break it into rectangles and triangles, run each one through the calculator, and add the rolls together.

I always marked out the beds before I measured, never after. A lawn shrinks once the borders go in, and it is the measurements taken before the borders that leave people with ten rolls spare.

How Much Topsoil Do I Need Under Turf?

Topsoil under new turf is 150mm deep on bare or poor ground, and that depth is what the calculator starts on. The sum is square metres times depth in mm, which gives litres, plus 15% for the soil settling.

For a 5m x 4m new lawn that is 20 x 150 = 3,000L, plus 15%, so about 3,450L. That is five 700L builders bags of Premium Lawn Soil Mix, £745 on today's shop prices, and about 41 wheelbarrow loads to move.

Where the soil already there is good, a 25mm layer raked over it is enough to give the turf a clean, even bed to root into. The same 5m x 4m lawn then takes about 575L, one builders bag.

Every soil figure in the table includes 15% for settlement. Loose tipped loads start at 15m³ (15,000L), so at 100m² and 150mm deep call us and we will price one. Topsoil settles 10% to 15% when it is screened topsoil, and more when it is a compost-rich blend. Firm it lightly and rake it level before the turf arrives, so most of the sinking happens before the lawn goes down.

Do You Need New Topsoil Before Laying Turf?

New topsoil before turf is only needed where the ground is poor, stony, too low or missing altogether. Good garden soil that drains, has a crumbly feel and sits at the right level just needs preparing. Preparing it means stripping the old grass and weeds, turning or rotavating the top 15cm, picking out the stones, raking it level and firming it lightly without over-compacting it. Turf grasses do best at a pH of about 6.5 to 7.0, so a quick soil test is worth it on ground you have never grown a lawn on.

That is where the 25mm option comes in. It does not replace bad soil. It gives the turf a fresh, fine, level surface to sit on, and it hides the stones and dips you missed with the rake. If you are not sure which you have, what makes good quality topsoil covers what to look for, and improving problem soils covers clay, compaction and the rest.

Turf Laid Over Builders' Rubble

Turf laid over builders' rubble on a new build almost always fails, because the roots have nowhere to go. New-build gardens often have clay subsoil on top, hidden under poor turf, with broken brick, waste mortar and cement bags beneath.

Dig a trial pit before you order anything, because one hole tells you what you are dealing with. If the topsoil is a thin skin over rubble, the rubble comes out and the full 150mm of topsoil goes back in. Nine times out of ten the picture is the same: green for one summer, then brown patches in every dry spell, right where the rubble sits highest. More turf does not fix it. More soil does.

Topsoil, Premium Lawn Soil Mix or Divot Mix: Which Goes Under Turf?

Premium Lawn Soil Mix is the bed made for new turf, topsoil builds up ground that needs a lot of new soil, and divot mix is for repairs and filling dips. All four of ours are in the calculator.

I would rather lay turf on a bed made for the job than on anything clever. The sand in Premium Lawn Soil Mix keeps the surface draining, and the soil in it holds the water new roots need in their first few weeks.

Getting the Level Right Next to Paths and Patios

Topsoil next to a path or patio finishes about 25mm below the paving, so the laid turf ends up level with it. A turf roll carries its own thin layer of soil and roots, and that is the gap it fills. Rake the soil flush with the paving and the lawn sits proud of it. The mower clips the edge every week and the turf there dries out first. Allow for the settlement too: soil raked exactly 25mm below the edge on day one will be lower a month later if it was not firmed.

When to Lay Turf Once It Arrives

Turf needs laying within 24 hours of delivery, and within 6 hours in hot weather. Once it is cut and rolled it starts to heat up and dry out. So the topsoil is delivered, spread and levelled before the turf is ordered, never after. Turf usually comes on a pallet to the kerbside, so work out where the lorry can set it down before you book it. Once it is down:

1. Water it straight after laying, until the soil under the rolls is soaked.
2. Keep it heavily watered for the first 3 to 4 weeks while it roots in.
3. Keep off it for at least 2 weeks.
4. Leave the mower in the shed until the roots have taken hold.

Spare turf cannot be sent back, which is one more reason to measure carefully and stick to the 5% to 15% extra.

Next Steps

Measure the lawn, run it through the calculator above, and decide on the soil first. The turf is the quick part of the job. Our topsoils are all on the topsoil range, and the calculator's Take me there buttons open each one with your measurements already filled in. For beds and borders rather than lawns, the topsoil calculator covers the other depths.

If you would rather talk the topsoil for your new lawn through with a person, call Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

Have you ever laid a new lawn from turf? How much extra did you order, and did the soil sink more than you expected? We would love to hear how it went.

FAQs

How many rolls of turf do I need for 100m²?

A 100m² lawn needs 105 rolls of turf with 5% extra for a straight-sided shape, or 110 rolls with 10% where there are curves and beds. Each roll covers 1m².

How much topsoil do I need for 100m² of turf?

Topsoil for 100m² of new turf comes to about 17,250L at 150mm deep with 15% for settlement. Over good existing topsoil, a 25mm layer is about 2,875L.

Can I lay turf straight onto my existing soil?

Turf can go straight onto existing soil when that soil is decent, drains well and has been loosened, cleared of stones and raked level. A 25mm layer of fresh topsoil on top gives it a cleaner bed to root into.

How long can turf be left before laying?

Turf needs to be laid within 24 hours of delivery, and within 6 hours in hot weather, because rolled turf heats up and dries out fast. Have the topsoil down and levelled before you order the turf.

Why is my new turf turning brown?

New turf turning brown in its first weeks is nearly always short of water, especially in a dry spell. Keep it heavily watered for the first 3 to 4 weeks while it roots in.

Is topsoil cheaper in bulk bags or small bags?

Topsoil in bulk bags usually works out cheaper per litre than packs of small bags, but small bags go where a bulk bag cannot. The calculator compares both on our live prices and shows the cheapest.