Tile Calculator (Tiles, Boxes, Grout and Thinset)

Enter the area (or room size), the tile size, joint width and tile thickness, and this calculator gives the tiles to buy with waste, the boxes, the grout in pounds from the standard joint-volume formula used by grout makers, and the 50 lb bags of thinset for your trowel. It works in inches or millimetres, so 300 mm porcelain and 3 × 6 in subway tile are equally easy.

Tile, grout and thinset calculator

How it works

Tiles = area ÷ ((tile length + joint) × (tile width + joint)), plus waste
Grout volume per sq ft = 144 × (L + W) ÷ (L × W) × joint width × joint depth, in cubic inches, with the tile thickness as the joint depth
Grout weight = volume × 0.0578 lb per cu in (about 1.6 kg per litre for dry cement grout, the density grout calculators use), plus 10%
Thinset = area ÷ coverage per bag: about 80 to 90 sq ft per 50 lb bag with a 1/4 in square notch, 60 to 65 with 1/4 × 3/8, 40 to 45 with 1/2 in

Worked example

A 12 × 10 ft floor in 12 × 12 in tile, 3/8 in thick, with 1/8 in joints, 10% waste, 15 sq ft per box:

Units: Feet and inches
Measure by: Length and width
Length: 12 ft
Width: 10 ft
Tile length: 12 in
Tile width: 12 in
Tile thickness: 0.375 in
Grout joint width: 0.125 in
Waste: 10%
Coverage per box (0 to skip): 15 sq ft
Thinset coverage per 50 lb bag: 85 sq ft

The calculator gives:

Tiles to buy: 130 (118 laid + 10% waste)
Boxes: 9 at 15 sq ft per box
Grout: 8.6 lb (3.9 kg) with 10% extra; one 10 lb box
Thinset: 2 × 50 lb bags at 85 sq ft per bag
Area: 120 sq ft (11.15 m²), 0.98 tiles per sq ft with the joint

Just under 118 tiles cover the floor; with waste, 130 tiles or nine boxes. The joints hold about 7.8 lb of grout, so buy 10 lb. Two 50 lb bags of thinset with a 1/4 in square-notch trowel. Switching to 3 × 6 in subway tile with 1/16 in joints on the same floor would need about 930 tiles and 9.7 lb of grout: small tiles mean far more joint.

Material and waste notes

Waste: 10% for a straight lay, 15% on a diagonal or with many cuts, more for herringbone. Patterned or large tile: buy an extra box for future repairs.
Joint depth is taken as the full tile thickness. Rectified tiles with very tight joints use very little grout, so a 10 lb box goes a long way.
Large-format tile (15 in or more on a side) needs a large-format mortar, a deeper notch and back-buttering, which roughly halves thinset coverage.
Uneven substrates eat thinset. Coverage figures assume a flat floor.
Boxes are sold whole; the box coverage on the carton is the one to use.

Frequently asked questions

How many 12×12 tiles for 120 square feet?

About 118 tiles laid with 1/8 in joints, so 130 with 10% waste (9 boxes of 15 sq ft).

How much grout for 100 square feet?

Depends on tile size and joint width. 12 × 12 in tile with 1/8 in joints, 3/8 in thick, needs about 6.5 lb per 100 sq ft; 3 × 6 in subway tile with 1/16 in joints about 8 lb.

How many square feet does a 50 lb bag of thinset cover?

Roughly 80 to 90 sq ft with a 1/4 in square-notch trowel, 60 to 65 with a 1/4 × 3/8 in notch, and 40 to 45 with a 1/2 in notch. Check the bag.

How much extra tile should I buy?

10% for straight layouts, 15% for diagonal or rooms with many cuts, and a spare box for repairs later; dye lots change.

Sanded or unsanded grout?

Unsanded for joints under 1/8 in and for polished or glass tile that sand would scratch; sanded for 1/8 in and wider.

Sources

Last reviewed: 26 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.