How Much Tile, Grout and Thinset Do I Need?

Tiling is one of the places where running short really hurts. The tile you need may be discontinued, or come from a different production lot with a slightly different shade. So the first rule is simple: work out the area, add 10% for waste, and buy it all at once. The second rule is that grout and thinset are estimated separately, and they depend on the size of the tile.

Step 1: Measure the area

Multiply length by width for each rectangle you are tiling, in feet, and add them up. Subtract areas that will not be tiled, such as a tub or a vanity, but do not subtract things like toilets, since you will be cutting tile around them. A 12 × 10 ft floor is 120 ft².

Step 2: Add waste

Every tile job has waste: edges that need cutting, tiles that chip, and tiles with a defect. The waste factor depends on the layout and the tile:

The extra also gives you a spare for repairs later. Keep the leftovers and note the lot number.

Step 3: Count tiles and boxes

Each tile covers its own area plus one grout joint. For 12 × 12 in tiles with a 1/8 in joint, one tile (with joint) is 12.125 × 12.125 in = 1.021 ft². For 120 ft² with 10% waste (132 ft²) you need 132 ÷ 1.021 = 130 tiles. If a box holds 10 tiles, that is 13 boxes. Always round up to a whole box.

Grout: how much?

Grout fills the joints, so the amount depends on the joint width, the depth of the joint (the tile thickness), and how many joints there are (which depends on tile size). Small tiles have many more joints per square foot, so mosaics use far more grout than large tiles do. Approximate grout needed per 100 ft², including 20% for waste and uneven backs:

The formula behind this is: pounds = area × (L + W) ÷ (L × W) × joint width × tile thickness × 8.34 × 1.2, with the tile and joint measured in inches and the 8.34 coming from grout density. Use the tile calculator to enter your own tile, and buy a little extra grout, since it is cheap and a second batch may not match the first.

Sanded grout is for joints 1/8 inch and wider. Use unsanded grout for narrow joints (under 1/8 in) and for delicate surfaces that sand could scratch. Epoxy grout is more stain-resistant and stronger, but it is harder to work with and costs more.

Thinset: how much?

Thinset is the mortar that bonds the tile to the floor. How much you use depends on the trowel notch, which depends on the tile size, and on how flat the surface is. As a guide, a 50 lb bag covers about:

• 90 to 95 ft² with a 1/4 × 1/4 in square-notch trowel (small tiles and mosaics).
• 60 to 70 ft² with a 1/4 × 3/8 in trowel (tiles up to about 12 in).
• 40 to 50 ft² with a 1/2 × 1/2 in trowel (large-format tile and uneven substrates).

Large tiles typically need "back-buttering", a thin layer on the back of the tile too, which uses more. Buy an extra bag if the floor is uneven, since levelling takes more mortar.

What else to buy

• Backer board or uncoupling membrane in wet areas and over wood subfloors.
• Tile spacers, a notched trowel, a grout float and sponges.
• Sealer for natural stone and for cement-based grout.
• Caulk (not grout) where tile meets a different material, a tub or a change of plane.
• Transition strips where the tile meets another floor.

Tips from experienced tilers

• Open several boxes and mix the tiles as you lay them. Slight shade variations are then spread out instead of making patches.
• Do a dry layout before you spread any thinset, so you can adjust the starting line and avoid skinny cuts at the edges.
• Check the floor for flatness. Large tiles are very unforgiving of dips and humps.
• Let the thinset cure for the stated time before grouting, and the grout before sealing or walking on it.