How to use the tile calculator
- Enter the length and width of the area to tile.
- Enter the tile width and length in inches.
- Enter the grout joint width.
- Choose a waste allowance: about 10% for straight layouts, more for diagonal or large-format tiles.
- Enter how many tiles come in a box.
Keep a few spare tiles from the same batch after the job; Decoratoradvice suggests this because matching tiles are hard to find later.
Tile formula
Area to tile = length × width
One tile's footprint = (tile width + joint) × (tile length + joint)
Tiles = area ÷ footprint × (1 + waste), rounded up
Boxes = tiles ÷ tiles per box, rounded up
Each tile takes up its own size plus one joint in each direction, which is why the joint width is added.
Worked example
An 8 × 5 ft bathroom floor in 12 × 24 in tiles, ⅛ in joints, 10% waste, 8 tiles per box:
Area: 40 sq ft = 5,760 sq in
Footprint: 12.125 × 24.125 = 292.5 sq in
Tiles: 5,760 ÷ 292.5 = 19.7
With 10% waste: 21.7, so 22 tiles
Boxes: 22 ÷ 8 = 2.75, so 3 boxes
Tiles per square foot
Approximate, with ⅛ in joints and no waste:
| Tile size | Tiles per sq ft |
|---|---|
| 3 × 6 in (subway) | 7.5 |
| 6 × 6 in | 3.8 |
| 12 × 12 in | 0.98 |
| 12 × 24 in | 0.49 |
| 24 × 24 in | 0.25 |
Tips
- For a backsplash, measure each section between cabinets, windows and outlets separately, then add them.
- Dry-lay a row before setting to check where cuts will fall; adjust the starting line so you do not end with a thin sliver.
- Buy all tiles from the same lot number.
- Work out grout at the same time with the grout calculator, using the same tile size and joint.
Common mistakes
- Ignoring the joint. On small tiles, joints make a noticeable difference to the count.
- Too little waste on large tiles. One broken 24 × 24 in tile is a lot of floor.
- Forgetting the tile thickness when planning transitions to other floors. The flooring calculator covers plank floors next door.
Frequently asked questions
How many tiles do I need for 100 sq ft?
With 12 × 12 in tiles and ⅛ in joints, about 98 tiles, or 108 with 10% waste.
How much extra tile should I buy?
About 10% for straight layouts. Diagonal patterns, herringbone and large-format tiles usually need more.
Does the grout joint really matter?
Yes. With 3 × 6 in subway tile, a ⅛ in joint reduces the count by about 6% compared with ignoring it.
How do I calculate tile for a shower?
Calculate each wall separately (width × height) and add the floor, then enter the total area with the length and width set to give that total.
Should I tile under cabinets?
Not usually under fixed base cabinets. Measure only the floor that will be visible, plus a little under the toe kick.
What else will I need?
Thinset, grout, spacers and edge trim. The baseboard calculator covers trim for floors that meet walls.
Key takeaways
- Tiles = area ÷ ((tile width + joint) × (tile length + joint)), plus waste.
- Allow about 10% extra, more for diagonal and large-format tile.
- Round tiles and boxes up.
- Calculate grout with the same tile size and joint.