Tile Calculator
Enter the area and your tile size to get the tile count, the number of boxes to buy, and the square footage to quote — with the grout joint and a cut allowance included, which is where most tile estimates go wrong.
How to use this calculator
- Measure the area, room by room. Do not average an L-shaped floor into one rectangle: split it, run the calculator twice, and add the boxes. Skip the area under permanent cabinets but include the area under appliances you might one day pull out.
- Enter the true tile size. A "12 × 24" tile is usually a hair under that nominal figure. Use the actual size printed on the box if it is given.
- Set the grout joint. This matters more than people expect. On a 4 × 4 in tile a 1/8 in joint reduces the tile count by about 6%; on a mosaic sheet, the joints are most of the area.
- Choose the allowance. 10% for a plain rectangular room with straight cuts, 15% for diagonal layouts and rooms with several corners, 20% for herringbone and other patterns where every tile is cut twice.
- Buy by the box. Tile is sold in whole boxes, so the tool rounds up and tells you how many spare tiles you will be left holding.
The formula
The key idea is that each tile occupies its own size plus one grout joint, because a joint sits on one side of every tile:
effective tile area (sq ft) = (tile width + joint) × (tile length + joint) ÷ 144
144 is the number of square inches in a square foot. Then:
| Step | Calculation |
|---|---|
| Tiles to cover the area | area ÷ effective tile area |
| With cut allowance | ceiling( tiles × (1 + waste%) ) |
| Boxes | ceiling( tiles ÷ tiles per box ) |
Both roundings go up, and they compound: 122 tiles at 8 per box means 16 boxes, so you actually take home 128.
Worked example
A 12 × 10 ft floor in 12 × 24 in tile with 1/8 in joints, 10% allowance, 8 tiles per box:
- Area: 12 × 10 = 120 sq ft
- Effective tile: (12 + 0.125) × (24 + 0.125) ÷ 144 = 2.032 sq ft
- Tiles to cover: 120 ÷ 2.032 = 59.1 → 60
- With 10%: 59.1 × 1.10 = 65.0 → 65 tiles
- Boxes: 65 ÷ 8 = 8.1 → 9 boxes (72 tiles, 12 spare)
Note how the box rounding gave you the allowance almost for free — this is common with large tiles, and it is a good reason to check the box count before paying for a 20% allowance you were going to get anyway.
How much extra tile to buy
| Layout | Allowance | Why |
|---|---|---|
| Straight lay, square room | 10% | Perimeter cuts only |
| Straight lay, many corners or niches | 12–15% | More part-tiles, more breakage |
| Diagonal / 45° | 15% | Every edge tile is a triangle |
| Herringbone, chevron, basketweave | 20% | Two cuts per edge tile |
| Large-format (24 in and up) | 10–15% | Fewer cuts but costly breakage |
If your tile is a discontinued or clearance line, add a full extra box regardless of layout — you cannot come back for one more.
Frequently asked questions
How much extra tile should I buy?
Ten percent over the measured area for a straight layout in a rectangular room, 15 percent for diagonal layouts or rooms with many corners, and 20 percent for herringbone and similar patterns where nearly every edge tile needs two cuts. Round up to whole boxes after that.
Does the grout joint change how many tiles I need?
Yes, and the smaller the tile the more it matters. Each tile effectively occupies its own size plus one joint width, so on small tiles the joints add up to a noticeable share of the floor. On a 4 by 4 inch tile a 1/8 inch joint cuts the tile count by roughly 6 percent; on a 24 inch tile the same joint changes almost nothing.
How many 12x24 tiles are in a box?
Most 12 by 24 inch porcelain comes 8 tiles to a box, covering about 15.5 square feet, but it varies by manufacturer between 6 and 8. The box states both the piece count and the coverage, and the coverage figure is the one to trust.
Should I include the area under kitchen cabinets?
No for base cabinets that are staying, since tile under them is wasted money and can complicate the install height. Yes for the area under a freestanding range or dishwasher, because the appliance will eventually be pulled out and an untiled gap there is both visible and a trip hazard for the new unit.
What do I do with leftover tiles?
Keep them, ideally a full box, stored flat and dry. Tile is produced in dye lots that shift between runs, so a replacement bought two years later rarely matches. Spare tiles turn a cracked-tile repair from a whole-floor problem into an afternoon.
Guides
- How Much Extra Tile Should You Buy?
- How to Plan a Tile Layout Before You Start
- How Much Thinset Do I Need?
- How Much Grout Do I Need?
- Can You Tile Over Existing Tile?