How to use the tile calculator
- Measure the length and width of the surface and choose the unit. For an L-shaped room, split it into rectangles, run each one, and add the results, or total the area with the square feet calculator.
- Enter the tile size as sold (for example 12 × 24 in) and the grout joint width recommended for that tile.
- Choose the layout pattern and a waste allowance. Diagonal and herringbone layouts produce more offcuts.
- Enter how many tiles come in a box and, optionally, a price to see the estimated tile cost.
How the calculation works
Each tile covers its own face plus half of the grout joint on every side, so the area one tile effectively covers is (tile length + joint) × (tile width + joint). Dividing the surface area by that module area gives the number of tiles for a perfect layout. The waste allowance is then added and the result is rounded up to a whole tile, and the box count is rounded up to whole boxes.
All measurements are converted to metres internally using exact factors, so you can mix, for example, a room measured in feet with tiles sized in centimetres.
Formula
- A
- Surface area (length × width)
- w
- Waste allowance as a decimal (10% = 0.10)
- tL, tW
- Tile length and width
- g
- Grout joint width
- ⌈ ⌉
- Round up to the next whole number
Worked examples
A 12 × 10 ft kitchen floor with 12 × 12 in tile
Area = 12 × 10 = 120 sq ft. With a 1/8 in joint, each tile covers (12.125 in)² = 147.02 sq in = 1.0210 sq ft.
120 × 1.10 ÷ 1.0210 = 129.29 → 130 tiles. At 10 tiles per box that is 13 boxes.
A 3 × 2 m bathroom wall with 30 × 60 cm tile
Area = 6 m². With a 3 mm joint, each tile covers 0.303 × 0.603 = 0.1827 m². 6 × 1.15 (diagonal: 15%) ÷ 0.1827 = 37.77 → 38 tiles.
Assumptions and limitations
- Openings such as doors, tubs or cabinets are not subtracted automatically; reduce the dimensions or enter separate areas.
- Waste allowances are rules of thumb. Irregular rooms, large-format tiles and patterned layouts can need more; keep a few spare tiles from the same production lot for future repairs.
- The cost covers tile only, not thinset, grout, underlayment, trim or labor.
- Box counts are based on the tiles-per-box figure you enter; check the carton, as counts vary by product.
Frequently asked questions
How much extra tile should I buy?
A common guideline is about 10% extra for straight and offset layouts and 15% or more for diagonal and herringbone layouts, because more tiles are cut at the edges. Small or oddly shaped rooms often need more.
Does the grout joint really change the tile count?
Yes, slightly. A 1/8 in joint around a 12 in tile increases the area each tile covers by about 2%, so you need a few fewer tiles than dividing by the tile face alone. The difference is bigger for small tiles and wide joints.
How do I calculate tile for a room that is not rectangular?
Divide the room into rectangles, calculate each one, and add the tile counts, or add the areas first with the square feet calculator and enter the total as a single rectangle (for example, length = total area, width = 1).
Should I round up to full boxes?
Yes. Most retailers sell tile by the box, and buying an extra box from the same lot is the safest way to match colour for future repairs.