Why does the calculator ask for the trowel notch instead of the tile size?

Because the notch is what actually meters the adhesive, and the tile size is only one of the things that decides the notch. Adhesive consumption is a depth of material over an area: a square-notch trowel leaves ridges covering roughly half the surface, so the mean bed is about half the notch depth, and the kilograms follow directly from that. Tile size matters because it dictates the notch — a mosaic on 3 mm, a 300 mm wall tile on 6 mm, a large-format floor tile on 10 or 12 mm — but so does the substrate: the same tile over a floor with a dip in it takes a bigger notch than over a flat one. Published tables that go straight from tile size to kilograms hide that second variable and then cannot explain the difference on site.

How much does back-buttering add?

About 30 per cent, the same figure the site's thinset page uses, and it is not optional as often as people assume. Back-buttering means skimming the back of each tile as well as combing the substrate, and it exists to close the voids that ridges leave. Most manufacturers require it above a certain tile size — commonly around 300 mm — and every wet area, external application and trafficked floor requires effectively solid bed, which is double the combed figure. The reason is not adhesion in the middle of the tile but the edges and corners: a void under a corner is where a tile cracks when something is dropped on it, and where water sits in a shower.

Why is my adhesive going further than this says, or not nearly as far?

Three things move real consumption more than anything in the arithmetic. The substrate: an unlevelled floor is being levelled with adhesive whether anyone intended it or not, and a 5 mm dip across a room is several bags nobody budgeted. The trowel angle: a trowel held at 45 degrees lays close to its rated notch, one held flatter lays much less, and two tilers on the same job routinely differ by a fifth. And the product: cement-based adhesives vary in density and in how much water they take, so a data sheet figure for the specific bag beats any general rate, including this one.

Does the grout come out of the same calculation?

No, and it scales with something completely different. Adhesive follows AREA, because it sits under the whole tile. Grout follows the length of the joints and their depth and width, which means it scales with the PERIMETER of each tile — so a floor of small tiles takes far more grout per square metre than the same floor in large format, while the adhesive barely changes. That is why the two are separate pages, and why a job that switches from 300 mm tiles to 600 mm ones roughly halves the grout and leaves the adhesive where it was, or raises it, because the bigger tile needs a bigger notch.

Renovation & Construction

Tile Adhesive Calculator

Work out how much tile adhesive an area needs from the trowel notch size and the bedding method, and how many bags that is.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Who is doing the work?

The standard allowance most suppliers and estimating guides assume for ordinary work.

Area to tile

The surface area being tiled.

Use the area of the SUBSTRATE, not the area of tile ordered. Cutting waste raises the tile count and not the adhesive: an offcut bedded into a corner uses the adhesive that was going under it anyway.

Trowel notch size

The notch depth of the trowel, which the tile size and substrate dictate.

If the adhesive data sheet names a notch for your tile, use that. Otherwise the notch rises with tile size and with how uneven the substrate is — a flat wall takes a smaller notch than a floor screed with a dip in it, for the same tile.

Bedding method

How the adhesive is applied.

Combed bed is adhesive on the substrate only. Back-buttering adds a skim to the back of each tile, which large-format work and most wall tiling over 300 mm require. Solid bed fills the ridges completely and is normally mandatory in wet areas, externally, and under anything trafficked by vehicles.

Waste allowance

Percentage added for adhesive left in the bucket and on the trowel.

Cement-based adhesive has a pot life, so a batch that stiffens before it is used is thrown rather than retempered. Ten per cent is normal on a straightforward job; raise it for small intricate areas where each batch is mixed and part-used.

Adhesive needed

149 lb

Medium confidence

About 3 x 50 lb bag(s). Check the figure against your adhesive's own data sheet for the notch you are using — formulations vary by roughly a fifth either side of this.

Mean bed depth: 0.12 in
Consumption rate: 0.61 lb/sq ft
Before waste: 135.18 lb
50 lb bags: 3 bags

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

ARDEX S27, S28 and X7 data sheets: about 1.0, 1.1 and 1.3 kg of powder per m² per mm of adhesive bed; S27 covers about 6.4 m² per 20 kg bag at a 3 mm bed, the bed a 6 mm square notch leaves (about 3.1 kg/m²)
CUSTOM Building Products VersaBond: data sheet TDS-119 (published 12/12/2023) gives 85-95 sq ft (7.9-8.8 m²) per 50 lb (22.68 kg) bag on a 1/4 in square notch, 2.6-2.9 kg/m²; the product page's coverage table gives 42-47 sq ft (3.9-4.4 m²) on a 1/2 in square notch, 5.2-5.8 kg/m². The rates here sit on ARDEX's line and a little above VersaBond's, so they err toward a spare bag
A square-notch trowel leaves ridges covering roughly half the surface at full notch depth, so the mean bed is about half the notch: 6 mm works out at about 3 kg/m² and 10 mm at about 5 kg/m², the same per-notch rates as the site's thinset-mortar calculator
Back-buttering and solid-bed work apply adhesive twice or fill the ridges completely, which is why the method is a multiplier on the combed figure rather than a separate rate

Inputs used

Area to tile: 220 sq ft
Trowel notch size: 6 mm — wall tile up to about 300 mm
Bedding method: Combed bed, floor or wall
Waste allowance: 10

Intermediate steps

Mean bed depth: 0.12 in
Consumption rate: 0.61 lb/sq ft
Before waste: 135.18 lb
50 lb bags: 3 bags

Final result148.7 lb

Confidence note: About 3 x 50 lb bag(s). Check the figure against your adhesive's own data sheet for the notch you are using — formulations vary by roughly a fifth either side of this.

What this calculation does not cover

The ridge factor of one half is a square-notch average. A U-notch or a half-moon trowel lays a different profile and consumes differently at the same nominal notch size, and neither is offered here.
Substrate absorbency is not an input. A dry, dusty or highly absorbent background pulls water out of the adhesive and is normally primed; an unprimed one takes more adhesive and bonds worse, and this figure assumes the background was prepared as the adhesive's data sheet requires.
A dip in the floor is filled with adhesive on real jobs and with nothing here. Adhesive is not a levelling compound and a substrate out of tolerance should be levelled first, but where it is not, consumption runs well above this figure and the excess is invisible to an area calculation.
One notch size and one method stand for the whole area. A job that is combed bed on the field and solid bed in the shower tray is two calculations, and running it as one will under-state the total.
Bag count assumes 20 kg bags and whole bags. Adhesives are also sold in 15 kg and 25 kg bags and as ready-mixed tubs rated by volume rather than weight, and none of those are the same arithmetic.
Only the adhesive is counted. Primer, levelling compound, decoupling matting, tanking and the grout are all separate items, and on a wet-room floor they can together exceed the adhesive.

Estimated cost — your price

Price per lb ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-26 · v1.1.0

Regulatory standards & verification citations4

ARDEX S27, S28 and X7 data sheets: about 1.0, 1.1 and 1.3 kg of powder per m² per mm of adhesive bed; S27 covers about 6.4 m² per 20 kg bag at a 3 mm bed, the bed a 6 mm square notch leaves (about 3.1 kg/m²)
CUSTOM Building Products VersaBond: data sheet TDS-119 (published 12/12/2023) gives 85-95 sq ft (7.9-8.8 m²) per 50 lb (22.68 kg) bag on a 1/4 in square notch, 2.6-2.9 kg/m²; the product page's coverage table gives 42-47 sq ft (3.9-4.4 m²) on a 1/2 in square notch, 5.2-5.8 kg/m². The rates here sit on ARDEX's line and a little above VersaBond's, so they err toward a spare bag
A square-notch trowel leaves ridges covering roughly half the surface at full notch depth, so the mean bed is about half the notch: 6 mm works out at about 3 kg/m² and 10 mm at about 5 kg/m², the same per-notch rates as the site's thinset-mortar calculator
Back-buttering and solid-bed work apply adhesive twice or fill the ridges completely, which is why the method is a multiplier on the combed figure rather than a separate rate

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To lay floor tile, tile a wall, cut ceramic and porcelain tile, grout and seal tiling and mix adhesive or mortar. Generic types, no brands, no prices.

Protection this work requires

Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.

Show the 15 tools this job needs

Essential

Chalk line
Grout float and sponge
Manual tile cutter
Mixing bucket or tub
Notched trowel
Paddle mixer
Spirit level
Tape measure

Recommended

Caulking gun
Rubber mallet
Tile nippers
Wet tile saw

Optional

Hole saw set
Laser level
Shovel and spade

Also needed as materials: caulk and sealant cartridges, chalk refill, diamond tile blades, grout sponges.

what each tiling tool is for, and the spec that decides which to buy where one does.

Called something else where you work? Tile adhesive — the term in each market, how close the equivalence really is, and the standard that governs it.

Already have some? How much wall tile will my tile adhesive fix?

How to calculate tile adhesive in 5 steps

Area to tileThe surface area being tiled.
Trowel notch sizeThe notch depth of the trowel, which the tile size and substrate dictate.
Bedding methodHow the adhesive is applied.
Waste allowancePercentage added for adhesive left in the bucket and on the trowel.
Adhesive neededThe tool computes the adhesive needed from those figures and shows the formula, its sources, and a confidence rating alongside it.

Adhesive needed by area to tile

Page defaults, not your figures above.

Area to tile	Adhesive needed (lb)
100 sq ft	67.6
150 sq ft	101
200 sq ft	135
250 sq ft	169
300 sq ft	203
350 sq ft	237
400 sq ft	270

Frequently asked questions

Why does the calculator ask for the trowel notch instead of the tile size?: Because the notch is what actually meters the adhesive, and the tile size is only one of the things that decides the notch. Adhesive consumption is a depth of material over an area: a square-notch trowel leaves ridges covering roughly half the surface, so the mean bed is about half the notch depth, and the kilograms follow directly from that. Tile size matters because it dictates the notch — a mosaic on 3 mm, a 300 mm wall tile on 6 mm, a large-format floor tile on 10 or 12 mm — but so does the substrate: the same tile over a floor with a dip in it takes a bigger notch than over a flat one. Published tables that go straight from tile size to kilograms hide that second variable and then cannot explain the difference on site.
How much does back-buttering add?: About 30 per cent, the same figure the site's thinset page uses, and it is not optional as often as people assume. Back-buttering means skimming the back of each tile as well as combing the substrate, and it exists to close the voids that ridges leave. Most manufacturers require it above a certain tile size — commonly around 300 mm — and every wet area, external application and trafficked floor requires effectively solid bed, which is double the combed figure. The reason is not adhesion in the middle of the tile but the edges and corners: a void under a corner is where a tile cracks when something is dropped on it, and where water sits in a shower.
Why is my adhesive going further than this says, or not nearly as far?: Three things move real consumption more than anything in the arithmetic. The substrate: an unlevelled floor is being levelled with adhesive whether anyone intended it or not, and a 5 mm dip across a room is several bags nobody budgeted. The trowel angle: a trowel held at 45 degrees lays close to its rated notch, one held flatter lays much less, and two tilers on the same job routinely differ by a fifth. And the product: cement-based adhesives vary in density and in how much water they take, so a data sheet figure for the specific bag beats any general rate, including this one.
Does the grout come out of the same calculation?: No, and it scales with something completely different. Adhesive follows AREA, because it sits under the whole tile. Grout follows the length of the joints and their depth and width, which means it scales with the PERIMETER of each tile — so a floor of small tiles takes far more grout per square metre than the same floor in large format, while the adhesive barely changes. That is why the two are separate pages, and why a job that switches from 300 mm tiles to 600 mm ones roughly halves the grout and leaves the adhesive where it was, or raises it, because the bigger tile needs a bigger notch.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.