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Thinset Calculator

Pick your trowel; the bags follow.

An estimate of quantity — coverage is one maker's, and back-buttering takes more.

1' 6" · 18 in · 1.5 ft · 0.4572 m

10' · 120 in · 10 ft · 3.048 m

15 ft²

Inch Calculator advises about 10% for tile laid straight, which is where this starts; 15% for diagonal, and Alpine 10-15% for herringbone. Mullican advises 5% for wood laid straight. It is added once, to whatever gets cut — the tiles or the planks, and the baseboard. A grout or mortar figure, where the page has one, is worked out on the surface as laid.

This page recalculates as you type. There is no Calculate button.

Answer

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Thinset

1 bags

15 ft² to tile · 9 tiles · 2 boxes

Buy 9 tiles
Boxes 2 × box of 8
Area to tile 15 ft²
Ticked items cost $87.00
More numbers
With the 10% for cuts 16.5 ft²
Grout 0.81 lb
DrawingThe project drawn to scale. Area 1: 1' 6" × 10'.1' 6"10'Area 1

Buying noteLarge tile wants mortar on the back of the tile as well as on the floor. Lift the first one back up and look at how much of it is covered before you set the rest.
Buying noteAt 1/8" buy sanded grout: unsanded is for joints under 1/8 in, and it cracks in a wider one. Our yield figure comes off the sanded chart, so this is the case it was worked out for.
Buying noteBuy the spare box with the rest, out of the same dye lot. A box bought a month later is a slightly different color, and nobody tells you until it is on the floor.

Breakdown

Surface Measurements Qty Area Share
Area 1 1' 6" × 10' Add ×1 15 ft²

What to buy

Buying noteLarge tile wants mortar on the back of the tile as well as on the floor. Lift the first one back up and look at how much of it is covered before you set the rest.
Buying noteAt 1/8" buy sanded grout: unsanded is for joints under 1/8 in, and it cracks in a wider one. Our yield figure comes off the sanded chart, so this is the case it was worked out for.
Buying noteBuy the spare box with the rest, out of the same dye lot. A box bought a month later is a slightly different color, and nobody tells you until it is on the floor.

Shopping list

2 2 × box of 8 $62.00 Reference price $23.50. Type your store's. Reference price $31.00. Type your store's. Reference price $29.50. Type your store's. Reference price $30.00. Type your store's. Reference price $33.00. Type your store's. Reference price $28.00. Type your store's. Reference price $26.00. Type your store's. Reference price $42.00. Type your store's.
1 1 × 10 lb bag $14.00 Reference price $24.00. Type your store's. Reference price $14.00. Type your store's.
1 1 × 25 lb bag $11.00 Reference price $17.00. Type your store's. Reference price $11.00. Type your store's.
Ticked items $87.00

Untick what you already have. Each row has its price beside it — type what your store charges.

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Standards

We hold the criteria and the clause, not the wording of the standard.

Not checked ANSI A108.02 · minimum joint width, as CTEF reads §4.3.8

A 1/8" joint clears the 1/16" minimum, which is as far as a measurement gets. The clause also asks for three times how much the tiles vary across their faces — lay a few out dry and look before you commit to the spacers.

Not checked ANSI A108.02 · large format minimum joint, as CTEF reads §4.3.8.1

A 1/8" joint is the minimum for rectified tile and under the 3/16" a calibrated tile needs. Which one you have is printed on the box — no measurement here can tell us.

Not checked ANSI A108.02 · mortar contact, as CTEF reads A108.02

This project tiles a wall, so the standard asks for 95% of the back of each tile in contact with mortar, against 80% in a dry area. It is measured by lifting a set tile back off — nothing on this page can judge it.

How this was worked out

Every number below is yours. Each constant links to the row where you can change it.

Area 1 1' 6" × 10' 15 ft²
With the waste for cuts 15 ft² × (1 + 10%) 16.5 ft²
One tile and its joint (12 in + 1/8") × (24 in + 1/8") ÷ 144 in²/ft² 2.0314 ft²
Tiles to buy 16.5 ft² ÷ 2.0314 ft² 9 tiles
Boxes to buy 9 tiles ÷ 8 tiles 2 × box of 8 · 7 tiles left over
Grout 15 ft² × 0.8336 in³/ft² (1/8" joints, 3/8" deep) × 0.0648 lb/in³ 0.81 lb → 1 × 10 lb bag

Change:Tile thickness, floor tileGrout in a cubic inch

Thinset 15 ft² ÷ 60 ft²/bag 1 bags → 1 × 25 lb bag

Change:Thinset coverage, 1/4 × 3/8 notchBag the coverage is published for

What it comes to 2 × $31.00 + 1 × $14.00 + 1 × $11.00 $87.00

Assumptions

Every one of these is editable. Change one and the answer changes with it.

Assumption Value Confidence
Tile thickness, floor tile3/8 in, the nominal body thickness of porcelain floor tile 12 in and larger, and the thickness Custom Building Products' coverage chart lists a 12 x 24 at. Grout sits as deep as the tile is thick, so this number scales the grout straight; measure yours and type it. ~ in Derived or single-supplier
Grout in a cubic inch25 lb of grout fills about 386 in³ of joint, worked back out of 30 cells of Custom Building Products' Polyblend Plus Sanded coverage chart. A bag holds one volume whatever tile it goes into, so this is a density rather than a per-size figure. ~ lb/in³ Derived or single-supplier
Thinset coverage, 1/4 × 3/8 notch60 to 67 ft² a 50 lb bag with a 1/4 × 3/8 in square-notch trowel (TDS-119), the commonest notch for a 12 in and larger floor tile. The low end is the figure here. ft²/bag From a data sheet or an agency document
Bag the coverage is published forThe bag the coverage figures below are published for. Custom Building Products' TDS-119 states VersaBond coverage per 50 lb bag, so a 25 lb bag covers half as much: coverage scales with weight, and the page solves the order in pounds rather than in bags for that reason. lb/bag From a data sheet or an agency document
Minimum joint1/16 in, the smallest grout joint ANSI A108.02 allows, and never less than three times the tile's facial dimension variation. Read in the Ceramic Tile Education Foundation's article on the clause, not in the standard itself - ANSI charges for the text. in From a data sheet or an agency document
Minimum joint, rectified large format1/8 in, the smallest joint for rectified tile with an edge over 15 in. A rectified tile is ground to size after firing, so its edges are square enough for a narrow joint; a calibrated one is not. in From a data sheet or an agency document
Minimum joint, calibrated large format3/16 in, the smallest joint for calibrated tile with an edge over 15 in. Whether a box holds rectified or calibrated tile is printed on the box and is not something any measurement on this page can say, which is why the check that reads this number never passes on its own. in From a data sheet or an agency document
Edge at which large format starts15 in: above this edge length the minimum joint stops being 1/16 in and becomes 1/8 or 3/16 in depending on how the tile was made. A 12 x 24 is over it on one side, a 12 x 12 is not. in From a data sheet or an agency document
Mortar contact, dry area80% of the back of the tile has to be in contact with mortar in a dry area. It is measured by lifting a set tile back up, not by any number on this page, so the page says the figure rather than judging it. Held as a percentage because that is how it is read and how the box shows it. % From a data sheet or an agency document
Mortar contact, wet area95% mortar contact in a wet area - a shower, a tub surround - and outdoors. The higher figure is why a shower wall project is told a different sentence from a kitchen floor. Held as a percentage because that is how it is read and how the box shows it. % From a data sheet or an agency document

How many bags of thinset

Thinset coverage depends on the trowel, not on the tile. A 1/4 by 3/8 inch square-notch trowel lays a thicker bed than a 1/4 by 1/4, and a 1/2 by 1/2 thicker again — so the same floor takes two bags, three bags or four depending on what is in your hand.

For the 120 square foot floor this page opens with, with the 1/4 by 3/8 notch most people use under 12 inch and larger tile: 2 bags of 50 pound VersaBond.

Coverage by notch

Trowel notch ft² a 50 lb bag 120 ft² takes
1/4 × 1/4 in square90–1002 bags
1/4 × 3/8 in square60–672 bags
1/2 × 1/2 in square42–473 bags
3/4 in U-notch at 45°34–384 bags

The ranges are Custom Building Products' own, from the VersaBond data sheet. This page works from the low end of each — at the high end you drive home a bag short.

Why the page does not pick the trowel for you

Because nobody publishes that mapping. There is plenty of advice about which notch suits which tile, and none of it comes with a number behind it, so putting one in would be inventing a constant and then hiding it. The trowel is a select, and it is the first thing to set.

As a rule of thumb a 1/4 by 3/8 square notch suits tile from 12 inches up, a 1/4 by 1/4 suits smaller tile and mosaic, and a 1/2 by 1/2 or a U-notch is for large format where the back of the tile needs a deeper bed. Check the tile's own instructions: many large-format tiles name a trowel on the box.

Back-buttering, and the 80 and 95 per cent

The number above is for mortar on the floor. Large tile usually wants mortar on the back of the tile as well — back-buttering — and that is more again, how much more depending on how flat the floor is.

The reason is coverage: the standard asks for 80% of the back of each tile in contact with mortar in a dry area and 95% in a wet one or outdoors. That is measured by setting a tile, lifting it straight back up and looking at what is on it. Nothing on this page can judge it, which is why the standards panel states the figure and asks you to check rather than passing you. Lift the first tile. It is the cheapest test in tiling.