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Tile Calculator

How many tiles a floor or wall needs — counting the grout joint, and the waste your layout actually causes.

Enter the area and the size of your tile.

1/8 in (0.125) is typical. It counts — especially on small tiles.

Boxes, price and waste

Leave blank to use the layout default.

Optional. Printed on the box.

Estimate. A real-world figure based on the assumptions listed below, which you can change.

How this calculator works

A tile does not occupy its nominal size. A 12-inch tile with a 1/8-inch grout joint takes up 12.125 inches, so it covers 147 square inches rather than 144. Ignoring that overstates the count by about 2% on a 12-inch tile — and by 12% on a 2-inch mosaic, where the joint is 6% of the tile in each direction. The joint is counted here, in both directions, once per tile because neighbours share it.

Waste is the other half of the answer, and it depends on the pattern rather than the room. A straight lay only cuts at the perimeter. A diagonal cuts every perimeter tile, and the offcuts are triangles that rarely fit anywhere else. Herringbone cuts twice per edge tile. The allowance therefore defaults to the layout — 10% straight, 15% diagonal, 20% herringbone — and stays editable, because these are trade rules of thumb rather than a standard.

Everything is rounded up, twice: once for the tiles that fit the area, and again for whole boxes if you are buying by the box. You cannot buy most of a tile, and you certainly cannot buy most of a box.

Order the whole lot at once. Tiles are made in batches and colours shift between them, so a box bought three weeks later can be visibly different in the same room.

The formula

Exactly what happens to your numbers, step by step.

  1. What one tile occupies

    footprint = (tile width + grout) × (tile height + grout)

    In inches. The joint is shared, so each tile carries one width of it, not two.

  2. Tiles

    tiles = ⌈area (in²) ÷ footprint⌉ × (1 + waste)

A worked example

A 10 ft by 10 ft floor in 12-inch tiles with a 1/8-inch joint, laid straight.

What you enter

Area
100 ft² (14,400 in²)
Tile
12 in × 12 in
Grout joint
1/8 in
Layout
Straight (10% waste)

The working

Footprint with the joint
12.125 × 12.125 = 147.0 in²
Tiles to cover
14,400 ÷ 147.0 = 98
Ignoring the joint would say
100
With 10% waste
98 × 1.10 = 108

108 tiles

Counting the joint saves two tiles here, which barely matters. Switch to a 3-inch mosaic and the same room needs about 1,470 tiles rather than 1,600 — a difference of 130 tiles, or several boxes. The smaller the tile, the more the joint is worth counting.

Assumptions

Every result here rests on these. Change your inputs and the result changes with them.

  • The area is a simple rectangle, or you have entered the square footage yourself.
  • One tile size throughout, with an even grout joint.
  • The waste allowance covers cuts, breakage and a few spares.
  • Boxes contain the number of tiles you enter.

What this cannot tell you

  • It does not lay out the room. A real tiler starts from a centre line and the offcuts depend on where the first tile lands — two rooms of identical area can need different numbers of tiles.
  • Borders, feature strips and mixed tile sizes are not modelled. Work those out separately and add them.
  • It does not know about batch variation. Order everything at once: tiles are made in batches and the colour shifts between them, which is visible in a finished floor.
  • Adhesive, grout, backer board and trim are not estimated. Those depend on the tile, the substrate and the notch size of the trowel.
  • Waste allowances are trade rules of thumb, not a standard. A room with many corners, an inexperienced tiler, or a very large-format tile all push them up.

Questions people ask

How many tiles do I need?

Divide the area by the size of one tile including its grout joint, then add waste for cuts. A 100 ft² floor in 12-inch tiles needs 98 to cover it and about 108 with a straight-lay allowance.

Does the grout joint really matter?

It depends entirely on the tile size. On a 12-inch tile a 1/8-inch joint changes the count by about 2%. On a 2-inch mosaic it changes it by 12%, because the joint is a much larger fraction of the tile. For small formats it is the difference between one box and two.

How much waste should I allow for tile?

About 10% for a straight lay, 15% for a diagonal, and 20% for herringbone — a diagonal cuts every perimeter tile and the triangular offcuts rarely serve twice. Add more for a room with lots of corners or if you are tiling for the first time.

Should I buy extra tiles?

Yes, and buy them at the same time. Beyond the cutting waste, keep a few spares for future repairs — replacing a cracked tile years later with a different batch is very obvious, because tile colour shifts between production runs.

What size grout joint should I use?

Commonly 1/16 to 1/8 inch for rectified tiles and 1/8 to 3/16 for standard ones, but it is the tile manufacturer’s specification that decides — pressed tiles vary enough in size that too tight a joint cannot absorb the difference.

Related calculators

Sources and review

Sources

  • Trade waste allowances by layout: 10% straight, 15% diagonal, 20% herringbone — rules of thumb rather than a standard

Methodology version 1.0.0 · Last reviewed