TryBuildCalcArtificial Grass Over Concrete Calculator (Bonded Installation on a Slab, Deck or Balcony)
Size turf, glue-down adhesive and underlay for a slab, deck or balcony.
🕒 Last updated: September 24, 2026
Inputs
Lawn Areas
Applies to every dimension on this form — lawn sizes in feet, and pile height, base depth and fastener spacing in inches. Switching converts the figures already entered rather than reinterpreting them.
ℹ️Sets a sensible starting point for the pile height, the infill type and rate, and the base depth — all of which you can then change. On a hard surface it also switches the whole installation to a bonded one, because there is nothing to nail into.
A fundamentally different installation: no excavation and no aggregate base, because the slab IS the base. The turf is bonded down with adhesive rather than nailed, since you cannot drive a nail into concrete, and a lighter infill is enough because nothing is being nailed through.
Area List
Add a row per rectangle. An L-shaped or curved lawn is best entered as the two or three rectangles it breaks into, measured to the widest point of each — that is how the turf gets cut anyway.
Area 1
Turf & Strip Layout
ℹ️The most important figure on this form. Turf is cut to length off a roll of fixed width, so the width decides how many strips your lawn needs and how much you pay for turf you cannot use. Check the actual roll width with your supplier before ordering.
ℹ️Most suppliers cut to length, so you pay for the linear metres or feet you need. Some sell full rolls only, in which case the order rounds up to whole rolls and the leftover is yours.
ℹ️Synthetic grass blades lean one way down the roll, so every strip in one continuous area must run the same way or the joint reads as a change of shade. That makes the running direction a single decision for the whole area — and it can change how much turf you buy by tens of percent.
Works out both directions for every area and uses the cheaper one, then tells you what the other would have cost. On an area whose width sits just over a roll width this is frequently a 15-30% difference in turf bought.
ℹ️The blade length. It sets how much infill is needed to hold the blades up, and it adds to the build-up depth you have to excavate for so the finished lawn sits flush with its edging.
ℹ️Spare length left at each end of every strip so it can be trimmed square to the edge. Added to both ends of each strip. Enter 0 to cut every strip exactly to length with nothing in hand.
ℹ️Extra on top of the strip layout, for trimming to curves, cutting around a tree or a manhole, and the piece that gets cut wrong. This is separate from the roll-width waste, which the layout already works out exactly — around 5% suits a simple rectangular lawn, 10% one with obstacles and curves.
When several areas each end in a narrow strip, those narrow pieces can be cut side by side out of one length of roll instead of one length each — they all still run with the pile, so it is a legitimate cut rather than a rotated offcut. Leave this off to keep each area on its own strips, which is simpler on site and harder to get wrong; turn it on to get the shared cut list and a smaller order.
Ground Preparation
Infill
ℹ️Infill weighs the turf down, holds the blades upright, shields the backing from UV and carries heat away. It is also the heaviest thing in the order by a wide margin, so it is bought by weight.
The default, and the cheapest by a distance. Rounded, kiln-dried grades flow between the blades instead of bridging; a sharp or unwashed sand packs and holds water. Published rates run about 1-2 lb/sq ft for a short residential pile and 2-3 lb/sq ft for a 1-2 in pile. Typical rate: 1-3 lb/sq ft.
ℹ️How much infill goes down per unit of lawn. Always check the turf manufacturer's own figure for your pile height — infill should sit in the bottom of the pile supporting the blades, not bury them. The result flags a rate that would do either.
Seams & Fixing
ℹ️The seam quantities come straight out of the strip layout, because a seam is exactly where two strips meet. If every area fits inside one roll width there are no seams at all and none of this is needed.
On a hard surface there is nothing to nail into, so the whole sheet is bonded down — adhesive is quoted by AREA here, not by seam length, and the perimeter and seams get a continuous bead.
The only option over concrete, a slab or decking. Nothing is driven into the surface — the turf is bonded, usually with a continuous perimeter bead and adhesive across the field.
ℹ️On a full glue-down the adhesive is spread over the whole surface, so it is quoted by AREA — a different figure entirely from the linear coverage of a seam bead.
Bends to a curve, which is what makes it the usual choice for a shaped lawn. Staked at roughly 3 ft centres.
Cost Estimation
Artificial Grass to Order
17.2 ft
5.2 m off a 15 ft (4.57 m) wide roll
Turf Area Bought
257.2 sq ft
23.9 m² / 28.6 sq yd, to cover 160 sq ft of lawn
16 ft x 10 ft lawn — 1 strip, 0 seams
Every area fits within a single roll width, so there are no seams at all.
Strips run along the length: 1 strip of 16.33 ft off a 15 ft wide roll.
The last strip only needs 10 ft of its 15 ft width, leaving a 5 ft x 16.33 ft offcut. You still buy the whole width, because the pile has to run the same way in every strip.
Where the Extra Turf Goes
| Lawn actually covered | 160 sq ft | 14.9 m² |
| Roll width bought but not covered Pure geometry: you buy whole roll widths, and the last is usually partial. The one component a layout change can remove. | +80 sq ft | 50% of the lawn |
| End trim at each strip end An allowance you set, not waste — spare length to cut square to the edge. | +5 sq ft | 245 sq ft running total |
| Cutting and fitting allowance (5%) For curves, obstacles and the piece that gets cut wrong. | +12.2 sq ft | - |
| Turf bought | 257.2 sq ft | 60.8% over the lawn area |
An area-based turf calculator reports only the last line as a flat 10% and misses the roll-width component entirely — which on this job alone is 80 sq ft.
Strip direction changes the order
Running the strips the other way round would have needed 65 sq ft more turf (6 m²). The cheaper direction was chosen for each area — set it out that way on site.
Infill
Kiln-dried silica sand (rounded) at 1 lb/sq ft (4.88 kg/m²): 160 lb / 73 kg (0.1 US tons)
That is 4 x 50 lb bag, about 1.6 cu ft of material, sitting roughly 0.12 in deep — 9.6% of the 1.25 in pile
Spread over the 160 sq ft of lawn, not the 257.2 sq ft of roll bought — offcuts never get infilled. Volume is estimated from a typical loose density of 100 lb/cu ft for this material; the purchase figure is always the weight.
Seams, Fixings & Accessories
Adhesive: 1 x 5 gallon bucket covering 160 sq ft of glue-down at 360 sq ft per pack, plus 52 ft of perimeter bead
Bender board (flexible plastic or composite): 3 x 20 ft for 52 ft of perimeter, plus about 19 stakes
Assumptions Used
Each area is laid out as whole strips cut off a 15 ft wide roll, with every strip in an area running the same way, because synthetic grass blades lean one way down the roll and a rotated strip reads as a different shade of green. That is why a partial last strip still costs a full roll width, and why offcuts are never rotated to fit. Each area's running direction was chosen to buy the least turf, with less seam breaking a tie. Seam length is taken as the full length of every joint between strips, which is where the tape, adhesive and seam-fastener quantities come from. Base aggregate, infill and any barrier or shock pad are sized on the 160 sq ft of lawn actually covered; turf is sized and priced on the 257.2 sq ft of roll bought. No aggregate base is included, since this is a bonded installation over an existing hard surface. Every whole-unit count — strips, rolls, bags, packs, boards — rounds up from unrounded values. This calculator estimates material quantity only. It does not design a drainage scheme, certify a playground fall height, assess subgrade bearing, or account for tree roots, service runs or existing structures.
Bill of Materials
Main material: 17.1 linear ft + recommended tools
+−
Bill of Materials
Main material: 17.1 linear ft + recommended tools
Computed quantities come from your own areas, roll width and material settings above; the consumables below are general recommendations, filtered to this installation — actual needs vary by product, ground conditions and site access.
For Your Job
Artificial grass
Infill — Kiln-dried silica sand (rounded)
Turf adhesive
Perimeter edging — Bender board (flexible plastic or composite)
General Tools & Consumables
Utility knife and plenty of spare blades
Chalk line or marking paint
Tape measure (long, 100 ft / 30 m)
Stiff broom, or a power broom for anything sizeable
Wheelbarrow
Gloves and knee pads
Bonding to a Hard Surface
Substrate cleaner and a stiff brush
Foam underlay or shock pad
Infill
Drop spreader
Plan drawn to the proportions of the dimensions entered, divided into the actual strips the layout needs; arrows show the pile direction every strip has to share, dashes mark the seams, and hatching marks roll width bought beyond the lawn edge. End trim at each strip end is included in the order but not drawn. Section layers are proportional to their real depths, with a minimum thickness so thin layers stay legible.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Artificial Grass / Synthetic Turf Calculator.
On a slab, the adhesive replaces the base and the nails
Laying turf on a hard surface is a genuinely different installation rather than the same one without the digging. There is no excavation and no aggregate base, because the slab is the base. Nothing can be driven into concrete, so the turf is bonded down instead — and that changes how the adhesive is quoted, from linear feet of seam to square feet of area, plus a continuous bead around the whole perimeter. The substrate has to be clean, dry and sound for any of it to hold; adhesive will not bond to a damp or dusty slab, and it will not bond to loose stone at all.
Two things are worth settling before you order. First, whether the existing surface already drains — turf backing passes water straight through, and with no base beneath there is nothing to take it away, so a slab that ponds will pond under the turf. Second, whether you want cushioning, because a foam underlay or shock pad is the only give a hard-surface lawn will ever have; over bare concrete the turf feels exactly as hard as the concrete. A lighter infill is enough here, since nothing is being nailed through and the adhesive is doing the holding.
Artificial Grass Formula & Method
Every figure is computed in feet, square feet, cubic feet and pounds, and converted only for display. Feet is the natural working unit because the governing quantity — roll width — is a fixed manufactured dimension, and because the layout is an integer count of those widths across a measured area.
Step 1 — Strip layout, per area
For strips running along dimension A, across dimension B:
strips = ROUNDUP( B / roll width )
strip length = A + 2 x end trim
roll length = strips x strip length
turf area = roll length x roll width
lawn area = A x B
seams = strips - 1
seam length = seams x A
width waste = (strips x roll width - B) x A
The ROUNDUP is the whole point. You buy whole roll widths, so a 16 ft wide lawn off a 15 ft roll takes two strips and you pay for the other 14 ft of the second strip. That is not a waste allowance, it is geometry — and it is reported separately from the cutting allowance for exactly that reason. Note that the seam runs the length of the AREA, not of the over-long strip.
Step 2 — Which way the strips run
Option 1: strips along the length
A = length, B = width
Option 2: strips along the width
A = width, B = length
Choose the option with the smaller turf area;
if equal, the one with less seam.
CONSTRAINT: every strip in one continuous area
must run the SAME way (pile direction).
Synthetic grass blades lean one way down the roll, so a strip laid at ninety degrees to its neighbour reads as a different shade of green from most angles — the same effect as nap on a carpet. That constraint is what makes the running direction a single decision for the whole area, and it is why the usual offcut-rotating tricks from tiling and flooring are unavailable here. On a lawn whose width sits just past a roll width, swapping the direction frequently changes the turf bought by 15-30%.
Step 3 — The whole job, and the allowances
roll length = sum over areas of
(strips x strip length x count)
order length = roll length x (1 + cutting% / 100)
order area = order length x roll width
whole rolls = ROUNDUP( order length / roll length )
Over-purchase, split into its three causes:
width waste — geometry, removable by layout
end trim — an allowance you set
cutting % — curves, obstacles, mistakes
Splitting the over-purchase matters because only the first component can be designed out. A single blended waste percentage hides the fact that a lawn a foot over a roll width is paying for a whole extra strip, which a small change to the layout would delete entirely. The cutting allowance is genuinely separate: around 5% for a simple rectangle, nearer 10% with curves and obstacles.
Step 4 — Base aggregate and excavation
compacted volume = lawn area x compacted depth
loose volume = compacted volume
-------------------------
(1 - compaction% / 100)
weight = loose volume x loose density
excavation depth = base depth
+ levelling course depth
+ pile height + backing
spoil (bulked) = in-situ volume x 1.20 to 1.30
The division is the part published turf calculators get backwards. At 20% compaction the loose volume needed is 25% more than the compacted volume, not 20% more — multiplying leaves the order about 4% short, which is enough to stop the job at the final lift. Excavation is the full build-up, not just the base: getting that wrong is the commonest reason a finished artificial lawn stands proud of its own edging. Dug soil bulks up, so size the skip on the bulked figure, not the hole.
Step 5 — Weed barrier, in overlapping strips
effective width = roll width - overlap
strips = ROUNDUP( area width / effective width )
length = strips x area length x layers
rolls = ROUNDUP( length / roll length )
layers = 2 for a separation layer below the base
AND a weed membrane above it
A membrane is also a fixed-width roll laid in strips, with one difference: the strips must overlap rather than butt, or weeds find the joint. So a 6 ft roll lapped 6 in contributes only 5.5 ft per strip, and dividing the lawn area by the roll's nominal area comes up short. Unlike turf, a membrane has no pile direction, so its strips are always run whichever way needs fewer of them.
Step 6 — Infill, seams and fixings
infill weight = LAWN area x rate (lb/sq ft)
infill bags = ROUNDUP( weight / bag weight )
infill depth = (weight / density) / lawn area
tape rolls = ROUNDUP( seam length / roll length )
adhesive = ROUNDUP( seam length / linear ft per pack )
or, glued down:
= ROUNDUP( area / sq ft per pack
+ perimeter / linear ft per pack )
perimeter fasteners = ROUNDUP( perimeter / spacing ) + 1
per area
field fasteners = ROUNDUP( area / spacing² )
edging pieces = ROUNDUP( perimeter / piece length )
Infill goes on the lawn area, never the roll area — offcuts are never infilled, and on a job with heavy layout waste the difference is a whole pallet. Adhesive is the one line with two different bases: a seam bead is quoted per linear foot of 12 in tape, a full glue-down per square foot of surface, and using one for the other is out by an order of magnitude. Perimeter fasteners are counted fence-post style, one at each end of a run as well as those between, applied per area because each lawn is its own closed loop.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Terrace | 16 ft x 10 ft (4.88 m x 3.05 m) |
| Application | Over concrete, decking or a balcony |
| Roll Width | 15 ft (4.57 m) |
| Strip Direction | Whichever wastes less (recommended) |
| Pile Height | 1.25 in (3.2 cm) |
| Allowances | 2 in end trim per strip end, plus 5% for cutting |
| Infill | Kiln-dried silica sand (rounded) at 1 lb/sq ft (4.88 kg/m²) |
| Seam Method | Full glue-down (over concrete or decking) |
Step 1 & 2 — Strip Layout, Both Directions
| Area | Calculation | Result |
|---|---|---|
| Terrace | ROUNDUP(10 / 15) = 1 strips of 16 + 2 x 0.17 = 16.33 ftThe other way round: 2 strips, 310 sq ft of turf | 245 sq ft of roll, strips along the length last strip uses 10 ft of its 15 ft width |
| Whole job | 1 strips across 1 area | 16.3 ft of roll = 245 sq ft |
Step 3 — Turf to Order, and Where the Extra Goes
| Calculation | Result |
|---|---|
| Lawn actually covered | 160 sq ft (14.9 m²) |
| (1 strips x 15 ft of width) less the lawn width, over the run | +80 sq ft roll-width waste (50%) |
| 1 strips x 2 x 2 in of end trim x 15 ft | +5 sq ft end trim |
| 16.3 ft x (1 + 5% cutting allowance) | 17.2 ft of roll |
| Order | 17.2 linear ft (5.2 m) = 257.2 sq ft bought, 60.8% over the lawn |
Step 5 & 6 — Infill, Seams and Fixings
| Calculation | Result |
|---|---|
| 160 sq ft x 1 lb/sq ft | 160 lb (73 kg / 0.1 US tons) of kiln-dried silica sand (rounded) |
| ROUNDUP(160 / 50) | 4 x 50 lb bag |
| (160 lb / 100 lb/cu ft) / 160 sq ft | 0.12 in deep — 9.6% of the 1.25 in pile |
| 0 seams x their strip runs | 0 ft of seam (0 m) |
| ROUNDUP(160 / 360 + 52 / 250) | 1 x 5 gallon bucket of adhesive |
| ROUNDUP(52 / 20) | 3 x 20 ft of bender board (flexible plastic or composite), about 19 stakes |
Figures above are rounded for display; the real quantities are always calculated from full, unrounded values.
Therefore, covering 160 sq ft of lawn (14.9 m²) takes 17.2 linear ft of 15 ft wide turf — 257.2 sq ft bought, 60.8% over the lawn area — laid as 1 strip with 0 seams, with 4 bags of infill.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.