How to use the tile calculator
- Choose US (feet and inches) or metric (meters and centimeters).
- Enter the area as length × width, or switch to total area if you already know the square footage. For an L-shaped room, add the parts in the square footage calculator first.
- Enter the tile size and the grout joint width.
- Pick a straight or diagonal layout. Leave waste blank to use 10% for straight and 15% for diagonal, or type your own.
- Enter how many tiles come in a box and, optionally, the price per box.
How the number of tiles is calculated
Each tile takes up its own size plus one grout joint in each direction, so the joint makes every tile cover slightly more floor. The waste allowance covers tiles you cut at the walls, around pipes and in doorways, plus a few breakages. A diagonal layout cuts a triangle off every tile along the edge, which is why it needs more. The calculator works in square inches (or square centimeters) so the tile and the room use the same unit.
Worked example
The defaults are a 10 × 12 ft floor, 12 × 12 in tiles with a 1/8 in joint, a straight layout and 10 tiles per box:
- Floor area: 10 × 12 = 120 sq ft = 120 × 144 = 17,280 sq in
- Area per tile: (12 + 0.125) × (12 + 0.125) = 147.02 sq in
- Tiles without waste: 17,280 ÷ 147.02 = 117.54
- With 10% waste: 117.54 × 1.10 = 129.29, rounded up to 130 tiles
- Boxes: 130 ÷ 10 = 13 boxes
With a diagonal layout and 15% waste, the count is 117.54 × 1.15 = 135.17, rounded up to 136 tiles (14 boxes). At $25 a box, the straight layout costs 13 × $25 = $325. In metric, a 3 × 4 m floor with 30 × 30 cm tiles and 3 mm joints needs 120,000 ÷ (30.3 × 30.3) × 1.10 = 143.8, so 144 tiles.
How much waste to allow
| Situation | Typical extra |
|---|---|
| Straight (grid) layout, simple room | 10% |
| Diagonal layout | 15% |
| Herringbone or other patterns | 15–20% |
| Large tiles (24 in / 60 cm and up), many corners or pipes | add 5% more |
Big tiles leave bigger offcuts that you often can't reuse, so they waste more than small ones in the same room. Mosaic sheets and small tiles cut cleanly and can go a little under 10%.
Common grout joint widths
Rectified porcelain tiles with precise, straight edges can use joints as narrow as 1/16 in (1.5 to 2 mm). Most floor tiles use 1/8 in (3 mm), and handmade or rustic tiles with uneven edges need 3/16 to 1/4 in (5 to 6 mm). The tile maker's packaging usually recommends a minimum joint. On small tiles, a wider joint noticeably reduces the tile count, while on large tiles it barely changes it.
Frequently asked questions
How many tiles do I need for 100 square feet?
With 12 × 12 in tiles and a 1/8 in joint, 100 sq ft needs about 98 tiles before waste, or 108 with 10% extra. For 18 × 18 in tiles the count drops to about 49 tiles with waste, and for 6 × 6 in tiles it rises to about 423.
Should I subtract the grout joint from the tile count?
You don't subtract it, you add it to the tile size. The calculator does this automatically, so each tile is treated as covering its own size plus one joint. With a 0 joint the result is the plain area divided by the tile area.
Why buy extra tiles?
You'll lose some to cuts and breakage, and a later repair is much easier if you have spare tiles from the same production batch. Tiles from a different batch can differ in shade, so most installers keep one box after the job.
How do I tile a room that isn't a rectangle?
Split the room into rectangles and other simple shapes, add up their areas, and enter the total with the total area option. Use the higher waste setting if the room has lots of corners, angled walls or built-in cabinets.
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