How much waste should I allow for tile?

Ten percent is standard for a straight lay in a simple rectangular room. Allow 15% for diagonal, herringbone or heavily cut layouts, and add a box of attic stock for future repairs.

Should I subtract door openings and cabinets?

Subtract areas larger than about 10 square feet, such as an island footprint. Small notches are already absorbed by the waste allowance.

What grout joint width should I use?

Rectified porcelain can go as tight as 2 mm, pressed ceramic usually needs 3 mm, and handmade or rustic tile with irregular edges may need 5 mm or more.

Does the calculator account for the pattern?

The tile count assumes a grid or offset lay. Diagonal and herringbone patterns produce more cuts, so raise the waste percentage rather than changing the tile size.

How do I estimate thinset as well?

Coverage depends on trowel notch, but a 1/4 in square notch typically covers 80–95 square feet per 50 lb bag. Large-format tile with a 1/2 in notch may cover only 40–50.

Trade Calculators

Tile Coverage Calculator

Tiles, boxes and grout volume for any room.

Inputs

Given

Unit system

Room length

Room width

Tile length

Tile width

Grout gap

Waste allowance

Tiles per box

Tile thickness

Results

Computed

Tiles to order

130

118 to cover the area plus 10% waste

Area to tile120.0 sq ft

Tiles before waste118

Boxes needed11

Joint coverage1.94% of surface

Grout volume1.73 litres

Approx. grout weight2.8 kg

Buy all boxes from the same production batch — shade and calibre vary between batches and the difference shows badly on a finished floor.

130 tiles · 11 boxes · 1.7 L grout

FIG. 2 — TILE LAYOUT WITH GROUT JOINT

How this is calculated

Tile counts are driven by the module size — the tile plus one grout joint — rather than the tile alone, because each tile occupies its own width plus the gap around it in the repeating pattern.

module area = (tile length + gap) × (tile width + gap)

tiles = area ÷ module area × (1 + waste %)

Box quantities are always rounded up, since suppliers rarely split boxes. Grout volume comes from the share of the surface taken up by joints, multiplied by the joint depth, which for a thin-set floor equals the tile thickness:

grout volume = area × joint fraction × tile thickness

Approximate grout weight assumes a cementitious grout at roughly 1.6 kg per litre. Epoxy grouts are denser and cover less per kilogram, so check the manufacturer coverage chart when using them. Wide-format tiles need proportionally less grout, while mosaics can need several times more than a standard floor of the same size.

Worked example

Tiling a 10 ft × 12 ft kitchen floor

Floor area = 120 sq ft, using 12 in × 12 in tiles (1 sq ft each) with a 1/8 in grout line.
Effective coverage per tile with the grout gap ≈ 1.02 sq ft, so the floor needs about 118 tiles.
Add 10% waste for cuts along walls and breakage: ≈ 130 tiles.
Tiles come 10 per box: order 13 boxes.
Grout for 1/8 in joints over 120 sq ft runs roughly 8–10 lb of sanded grout.

Common mistakes

Ignoring the grout joint
A 1/8 in joint on a 12 in tile changes coverage by about 2%. On small mosaics with wide joints the effect can reach 10% — enough to change the box count.
Using 10% waste for diagonal layouts
A diagonal or herringbone layout cuts every edge tile on the angle and typically wastes 15–20%. Straight-lay assumptions under-order patterned floors.
Forgetting the wet-area extra
Showers and tub surrounds deserve an extra box beyond the waste factor: future repairs need a dye-lot match, and the same tile may not be sold in five years.