Tile calculator: tiles, grout and thinset for floors and walls

Quick answer

For 80 sq ft of 12 × 12 in tile with 1/8 in joints, you need 78.4 tiles before any extra, or 87 with the 10 percent that tile sellers recommend for a straight lay; a diagonal lay calls for 15 percent and herringbone for 15 to 20 percent. The joints of that floor take about 5.2 lb of grout if the tile is 3/8 in thick, and one 50 lb bag of thinset covers 85 sq ft or more with a 1/4 × 1/4 in trowel.

What this calculator does

It counts the tiles that fit into an area when every tile is surrounded by a grout joint, adds an allowance for cuts and breakage that follows the laying pattern, and converts the result into boxes. It also estimates the grout that fills the joints and the bags of thinset or tile adhesive for the notch size of your trowel.

The area can be a floor (length and width), an area you already know, up to three walls of a shower to one tiled height less any niches, or a kitchen backsplash. For a tiled shower floor, calculate the floor separately: it usually uses a different, smaller tile.

It does not calculate backer board, waterproofing, trim pieces or edge profiles, and it does not lay out rows, so it cannot tell you where the cuts fall.

How to use it

1. Choose metric or US units. In US units you can type feet and inches, such as 5' 6", and fractions, such as 3/16.
2. Under What you measured, choose a floor, an area, shower walls or a backsplash, and enter the sizes the form asks for.
3. Enter the length and width of one tile, the width of the grout joint and the number of tiles in a box. Use the real size printed on the box.
4. Choose the laying pattern. It fills in the recommended extra, which you can change.
5. For grout and adhesive, enter the tile thickness (the depth of the joint), the bag size of your grout, the trowel notch and the coverage printed on the adhesive bag for that notch.
6. Select Calculate.

How the result is calculated

1. Floor: area = length × width. Shower: area = (back + left + right wall) × tiled height − niches × niche width × niche height. Backsplash: area = length × height.
2. Area of one tile with its joint = (tile length + joint) × (tile width + joint).
3. Tiles needed = area ÷ area of one tile with its joint × (1 + allowance ÷ 100), rounded up to a whole tile. Boxes = tiles ÷ tiles per box, rounded up.
4. Grout volume per square metre in litres = (tile length + tile width) ÷ (tile length × tile width) × joint width × tile thickness, all in millimetres. Grout weight = volume × weight of mixed grout. Bags are rounded up.
5. Bags of adhesive = area ÷ area one bag covers, rounded up.

The grout formula is the one that Mapei prints on its grout data sheets, with a weight factor of 1.6 kg per litre; BAL and UltraTile use the same formula with factors of 1.5 and 1.2 for their grouts. Grout and adhesive are calculated for the tiled area, without the allowance for cut tiles.

Worked example

A floor is 3 m long and 2 m wide, so the area is 6 m². The tiles are 300 mm by 300 mm with a 3 mm joint. One tile with its joint takes up 0.303 × 0.303 = 0.0918 m². Tiles without allowance: 6 ÷ 0.0918 = 65.4. With 10 percent for a straight grid: 71.9, rounded up to 72 tiles. With 10 tiles in a box: 7.2, rounded up to 8 boxes.

Grout for 10 mm thick tiles: (300 + 300) ÷ (300 × 300) × 3 × 10 = 0.2 L per m², so 1.2 L for 6 m², and at 1.6 kg per litre 1.92 kg, shown as 2 kg: 1 bag of 5 kg. Adhesive with a 10 mm notch at 5.2 m² per 20 kg bag: 6 ÷ 5.2 = 1.15, so 2 bags.

In US units: a floor of 10 ft by 8 ft has 80 sq ft. Tiles of 12 in by 12 in with a 1/8 in joint take up 12.125 × 12.125 = 147.0 sq in each, which is 1.021 sq ft. 80 ÷ 1.021 = 78.4 tiles, and with 10 percent allowance 86.2, rounded up to 87 tiles. With 10 tiles in a box, you buy 9 boxes.

Grout for 3/8 in thick tiles: (12 + 12) ÷ (12 × 12) × 0.125 × 0.375 = 0.0078 cubic inches per square inch, or 1.125 cubic inches per square foot; 80 sq ft take 90 cubic inches, 0.052 cu ft. At 99.9 lb per cu ft (1.6 kg per litre) that is 5.2 lb, shown rounded up as 5.3 lb: 1 bag of 25 lb. Thinset with a 1/4 × 1/4 in trowel at 85 sq ft per 50 lb bag: 1 bag.

Shower walls: a back wall of 5 ft and two side walls of 3 ft, tiled to 7 ft, are 11 × 7 = 77 sq ft. A niche of 12 × 20 in lined with a mosaic takes 1.67 sq ft out, leaving 75.3 sq ft: 82 tiles of 12 × 12 in with 10 percent extra, 9 boxes.

Extra tile for each laying pattern

Patterns at an angle to the walls produce more cut tiles, and tile sellers recommend more extra for them. The presets are the figures that several of them publish.

Some sellers are more cautious: Fireclay recommends at least 15 percent on every order, and Artistic Tile 20 percent or more. Increase the allowance for large tiles in small rooms, rooms with many corners, and natural stone with a lot of variation.

Grout, thinset and trowel size

Grout coverage depends mostly on the joint and the tile size: small tiles have far more joint per square foot. Grout makers publish charts made with the formula above. For a 12 × 12 in tile 3/8 in thick with 1/8 in joints, Mapei states 383 sq ft for a 25 lb bag of Keracolor S and Custom Building Products 348 sq ft for Polyblend Plus sanded grout. With 3/16 in joints the same tile covers 234 sq ft per bag (Custom).

Adhesive coverage depends on the notch of the trowel. Custom states 85 to 95 sq ft per 50 lb bag of VersaBond with a 1/4 × 1/4 in square notch and 60 to 67 sq ft with 1/4 × 3/8 in; Mapei states 38 to 45 sq ft with a 1/2 × 1/2 in notch for Ultraflex LFT Rapid. In metric, Davco (Australia) states about 6 to 7 m² per 20 kg bag of Ceramacrete with a 6 mm notch, and BAL (UK) 0.26 m² per kg, 5.2 m² per 20 kg bag, for a 10 mm solid bed. The 12 mm preset of 3.1 m² is Mapei's US figure converted to a 20 kg bag. The presets use the lower end of each range.

Which notch? Floor & Decor recommends 1/4 × 1/4 in for tiles up to 12 × 12 in and 1/2 × 1/2 in or larger for bigger tiles; Davco recommends 6 mm for 150 mm tiles, 10 mm for 300 mm tiles and 12 mm plus back-buttering from 400 mm. Coverage charts assume adhesive on the floor or wall only; back-buttering large tiles uses more, and Custom advises adding it to the estimate.

Joint width: the tile installation standard ANSI A108.02, as quoted by the Tile Council of North America, asks for a joint at least three times the size variation of the tile and never less than 1/16 in; for tiles with a side over 15 in, the average joint should be at least 1/8 in for rectified tile. Use the joint the tile maker recommends.

Showers and backsplashes

The International Residential Code, section R307.2 in the 2021 edition, requires shower walls to have a nonabsorbent finish to at least 6 ft above the floor. Many showers are tiled higher; enter the height you will tile.

A niche lined with a mosaic or a different tile is subtracted from the wall and bought separately. If the niche is lined with the same tile, enter 0 niches: the back of the niche needs about as much tile as the opening, and the sides are cut from what the allowance provides. Schluter sells prefabricated niches 12 in wide and 6, 12, 20 or 28 in high.

For a backsplash, measure the wall between the countertop and the wall cabinets. KraftMaid installs wall cabinets 19 1/2 in above the base cabinets, which leaves about 18 in above a 1 1/2 in countertop; the kitchen designers' association NKBA gives 15 in as the minimum clearance. Leave out windows and the space behind a range hood if they are not tiled.

Common mistakes

• Entering the nominal size of the tile. A tile sold as 12 × 12 inches or 30 × 30 cm can be a few millimetres smaller.
• Using the straight-lay allowance for herringbone or diagonal. Those patterns have a cut tile at every wall.
• Ordering the exact number. Tiles of a later batch can differ in shade and size.
• Estimating grout by area alone. A mosaic with 1/8 in joints needs several times the grout of a large tile.
• Using the thinset coverage for the wrong notch, or forgetting that back-buttering large tiles uses more.
• Adding the shower floor to the walls when it gets a different tile. Calculate each tile on its own.