Enter the size of the floor, wall or backsplash and the size of your tile. The calculator allows for the grout joint, adds extra for cuts and breakage and tells you how many tiles and boxes to buy.
How to use the tile calculator
- Measure the floor or wall and enter the length and width. Split an L-shaped room into rectangles and add the tile counts together.
- Enter the tile size as sold, for example 12 × 24 in, and the grout joint you plan to use.
- Pick the layout. Straight lay needs the least extra; diagonal, brick bond and herringbone layouts need more because of the angled cuts.
- Add the number of tiles per box from the carton to get a box count, and a price for a cost.
Tile formulas
Area (ft²) = length (ft) × width (ft) Tiles per ft² = 144 ÷ ((tile length + joint) × (tile width + joint)), all in inches Tiles = area × tiles per ft² × (1 + extra %), rounded up Boxes = tiles ÷ tiles per box, rounded up
Each tile takes up its own size plus one grout joint in each direction, so a 12 in tile with a 1/8 in joint fills a 12.125 in square. Ignoring the joint slightly overestimates the count; on small mosaic and subway tiles the joint makes a bigger difference.
Worked example: a 12 × 10 ft bathroom floor
- Area: 12 × 10 = 120 ft².
- Tiles per ft² for 12 × 12 in tile with a 1/8 in joint: 144 ÷ (12.125 × 12.125) = 0.979.
- Tiles before extra: 120 × 0.979 = 117.5.
- Straight lay, 10% extra: 117.5 × 1.10 = 130 tiles, or 13 boxes of 10.
Laid on the diagonal with 15% extra, the same floor takes 136 tiles.
Tiles per 100 square feet
With 10% extra for a straight lay:
| Tile size | Joint | Tiles per ft² | Tiles per 100 ft² | With 10% extra |
|---|---|---|---|---|
| 4 × 4 in | 0.0625 in | 8.73 | 873 | 960 |
| 6 × 6 in | 0.0625 in | 3.92 | 392 | 431 |
| 3 × 6 in subway | 0.0625 in | 7.76 | 776 | 854 |
| 12 × 12 in | 0.125 in | 0.98 | 98 | 108 |
| 12 × 24 in | 0.125 in | 0.49 | 49 | 55 |
| 18 × 18 in | 0.125 in | 0.44 | 44 | 49 |
| 24 × 24 in | 0.125 in | 0.25 | 25 | 28 |
| 6 × 36 in plank | 0.125 in | 0.65 | 65 | 72 |
How much extra tile should I buy?
Tile Mountain recommends 10% extra for a straight lay, where tiles run parallel to the walls and need the fewest cuts, and 15% for diagonal, brick bond and herringbone patterns, which create more cuts and offcuts. Add more for a room with many corners, pipes or a large tile that leaves big offcuts, and keep a few spare tiles after the job: matching a dye lot years later is often impossible.
Tips for buying tile
- Buy all the tile from one lot. Colour and size can vary between production runs; check the lot number on every box.
- Measure walls to the height you will tile. A backsplash is usually only 18 in high between counter and cabinets.
- Do not subtract small fixtures. A toilet or vanity footprint is small and the cuts around it use extra tile anyway.
- Plan the setting materials. Thinset and grout depend on the tile and trowel; follow the bag. The square footage calculator handles odd room shapes.
Questions
How many tiles do I need for 100 square feet?
About 98 tiles of 12 × 12 in before extra, and 108 with 10% extra. For 12 × 24 in tile it is 55 with 10% extra.
How do I calculate tiles for a wall?
Multiply the width of the wall by the height you will tile, subtract large openings such as a window, and enter that as the area.
Should I include the grout line?
Yes, for an accurate count. Leave it at 0 if you only want a quick upper estimate.
How much extra tile for herringbone?
About 15%, the same as for diagonal and brick bond layouts.
Sources
- How Many Tiles Do I Need? Tile Calculation Guide for Floors, Walls, and Bathrooms, Tile Mountain.
Used for: 10% extra for straight lay and 15% for diagonal, brick bond and herringbone. - NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Exact inch and foot definitions; square metre conversions.