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Trowelly

Tile Calculator

Enter the area to tile, the tile size and grout joint to see how many tiles, and optionally boxes, to buy.

Units
ft
ft
in
in
in
%

10% for straight layouts, 15% for diagonal or large-format tile.

Add prices for a cost estimate (optional)
each

Results

Tiles
44 tiles
Area
40 ft²
  • Includes 10% extra.

Where to buy

Quantities from your result, with links to search each store.

Your ZIP code stays on this device. We use it to show stores and suppliers in your area.

You may also need

Links search each store’s website. Check prices and stock before you go.

How to use the tile calculator

  1. Choose a Shape and enter the floor or wall dimensions.
  2. Enter the Tile length, Tile width and Grout joint in inches.
  3. Set the Extra for cuts & breakage: 10% for straight layouts, 15% for diagonal or large-format tile.
  4. Optionally enter Tiles per box to get a box count, and a price per tile.

How it works

Each tile covers its own size plus one grout joint in each direction. The calculator divides the area by that footprint, adds your extra for cuts and breakage and rounds up.

If you enter tiles per box, it also rounds the tile count up to whole boxes.

Area per tile (ft²) = (tile length + joint) × (tile width + joint) ÷ 144

Tiles = area ÷ area per tile × (1 + extra %), rounded up

Boxes = tiles ÷ tiles per box, rounded up

Worked example

With the default inputs, an 8 × 5 ft floor is 40 ft². A 12 × 12 in tile with a ⅛ in joint covers 12.125 × 12.125 ÷ 144 = 1.02 ft².

That is 39.2 tiles, or 43.1 with 10% extra, so buy 44 tiles. At 10 tiles per box, that is 5 boxes.

Tips before you buy

  • Buy all tile from the same lot and keep a few spares for future repairs.
  • Large-format and diagonal layouts waste more at the edges; use 15% extra.
  • Dry-lay a row before setting to plan cuts and avoid thin slivers at the walls.
  • Use cement board or a waterproofing membrane behind tile in showers and other wet areas.

Frequently asked questions

How many 12×12 tiles do I need per square foot?

With a ⅛ in grout joint, each tile covers about 1.02 ft², so slightly less than one tile per square foot before adding extra for cuts.

How much extra tile should I buy?

About 10% for straight layouts and 15% for diagonal patterns or large-format tile.

Does the grout joint affect how many tiles I need?

Yes, a little. Wider joints mean each tile covers more area. The effect is small for large tiles and larger for small tiles and mosaics.

How many tiles do I need for a 40 square foot bathroom?

Using 12 × 12 in tiles with ⅛ in joints and 10% extra, about 44 tiles. Smaller or rectangular tiles need a different count.

Results are estimates based on the measurements you enter and typical material properties. Products vary, so check quantities with your supplier and follow product labels and your local building codes. Read the full disclaimer. Last reviewed October 9, 2026.