How to use the tile calculator
- Add each area to tile as a length and width in feet. Mark openings you will not tile, such as a tub or vanity base, as Subtract.
- Enter the tile length and width in inches and the grout joint width in inches (0.125 is 1/8 inch).
- Keep the 10% layout waste or change it, and enter tiles per box from the carton label.
- Read the tiles to buy, the boxes, and the square foot cross-check. Add a price per tile or per box for a cost estimate.
Formula
Effective tile size = (tile length + joint) x (tile width + joint)
Tiles = area in square feet x 144 / effective tile size in square inches
Tiles with waste = tiles x (1 + waste percent), rounded up
Boxes = tiles with waste / tiles per box, rounded up
Cross-check coverage = tiles bought x effective tile size / 144
The 144 converts square feet to square inches. Each tile is counted together with one grout joint, which is why a wider joint reduces the tile count slightly.
Worked example: a 10 ft by 12 ft bathroom floor with 12 inch tile
The area is 10 x 12 = 120 sq ft. With a 1/8 inch joint each tile occupies 12.125 x 12.125 = 147.02 sq in.
Tiles = 120 x 144 / 147.02 = 117.54. A 10% waste allowance brings that to 129.29, so you buy 130 tiles.
At 10 tiles per box that is 13 boxes (130 tiles). The cross-check says 130 tiles cover 130 x 147.02 / 144 = 132.72 sq ft, which is your 120 sq ft plus the allowance.
At $28 per box the tile costs 13 x $28 = $364.00.
Why the grout joint changes the count
A tile and its share of grout take up slightly more room than the tile alone. For small mosaic tiles the effect is large, while for 12 inch tiles it is under 2 percent. Entering the joint width gives a more honest count, and setting it to 0 shows what the count would be for tight-fit or rectified tile.
Layout waste is a choice, not a constant
Straight lay patterns over a simple rectangle waste less than diagonal, herringbone or patterned layouts, and a room with many corners wastes more than an open one. A stock allowance of 10 percent is a reasonable starting point, but it is only an input here. Ask your installer what allowance their layout needs, and consider keeping a few extra tiles from the same production lot for future repairs.
Buying by box
Tile is sold in cartons, so the practical number is boxes. The tool rounds up to whole boxes and shows how many tiles that gives you. If the box label lists coverage in square feet instead of tiles, you can use the flooring calculator instead, which works from square feet per box. To combine several rooms into one area first, use the square footage calculator.
Assumptions and limits
- Every tile has the size you enter and a joint of the width you enter. Nominal sizes on boxes may differ slightly from real sizes.
- The layout is a plain grid. Offset, diagonal and patterned layouts change the waste, which you control with the allowance.
- The default tiles per box (10) is only a starting value. Use the number on your carton.
- Grout, thinset, backer board, trim and edge pieces are not calculated.
- This is a planning estimate. Confirm quantities with your supplier or installer before ordering.
Frequently asked questions
How many 12x12 tiles do I need for 100 square feet?
Without a joint and waste you need exactly 100 tiles. With a 1/8 inch joint and a 10 percent allowance it is about 108 tiles. Enter your numbers for an exact count.
Should I include grout lines in the calculation?
Yes, because each tile takes up its size plus a joint. The effect is small for large tiles and bigger for small mosaics, so this tool includes it by default.
How many extra tiles should I buy?
A common starting point is 10 percent, with more for diagonal or intricate layouts. The allowance is your choice, so set it to what your installer recommends.
Does this work for wall and backsplash tile?
Yes. Measure each wall section as a length and width, subtract windows or outlets that are large, and use the same tile size and joint inputs.
What if my tile box lists square feet and not tile count?
Divide the carton square feet by the area of one tile in square feet to get tiles per box, or leave tiles per box blank and use the tile count to buy by area.