How the tile calculator works
Tile is priced per square foot but bought by the box, and the number of boxes depends on four things: the area, the size of each tile, the width of the grout joints and how much you lose to cuts. The calculator takes the area (length × width, minus anything you won't tile), adds a waste allowance for the layout, and divides by the space one tile really covers: the tile plus half a grout joint on each side. It then rounds up to whole tiles and whole boxes, and prices the tile you actually carry home.
Waste by layout
| Layout | Waste | Why |
|---|---|---|
| Straight or 1/3 offset | 10% | Cuts along two walls, breakage, doorways |
| Diagonal (45°) | 15% | Triangular cuts along every wall |
| Herringbone | 20% | Angled cuts all around the perimeter |
The formula
tiles = area × (1 + waste %) ÷ [(tile L + joint) × (tile W + joint) ÷ 144], rounded up
boxes = tiles ÷ tiles per box, rounded up
grout (lb) = area × (L + W) ÷ (L × W) × joint × thickness × 144 ÷ 1,728 × 100 × 1.1
The grout line is the standard joint-volume method used by grout manufacturers: (L + W) ÷ (L × W) is the length of joint per square inch of tile, multiplied by the joint width and depth (the tile thickness) to get cubic inches of grout. We assume mixed grout weighs about 100 lb per cubic foot and add 10% for cleanup and mixing loss. Tile dimensions, joint and thickness are all in inches.
Example: a 10 × 12 ft floor in 12 × 24 in porcelain
Straight layout, 1/8 in joints, 3/8 in thick tile, 8 tiles per box at $3.00 per sq ft, and grout in 10 lb bags at $15.
| Step | Result |
|---|---|
| Floor area (10 × 12) | 120 sq ft |
| Plus 10% waste | 132 sq ft |
| One tile with joint (12.125 × 24.125 ÷ 144) | 2.031 sq ft |
| Tiles needed (132 ÷ 2.031 = 64.98) | 65 tiles |
| Boxes (65 ÷ 8 = 8.1) | 9 boxes |
| Tile bought (72 tiles × 2 sq ft) | 144 sq ft |
| Tile cost (144 × $3.00) | $432.00 |
| Grout (101.25 cu in, plus 10%) | 6.4 lb → 1 bag, $15.00 |
| Total materials | $447.00 |
Notice how little grout large tiles need. The same floor in 4 × 4 in tile with 1/8 in joints and 1/4 in thickness needs about 17 lb, because there is far more joint per square foot.
Tips before you buy
- Price by the square foot, count by the box. A carton of 12 × 24 tile usually holds 6 to 8 pieces (about 12 to 16 sq ft). Enter the exact count from the label.
- Buy one lot. Shade and caliber vary between production runs. Check that every box has the same lot number and blend tiles from several boxes as you lay them.
- Large tiles need flat floors. Tiles over 15 in on a side generally call for a flatter substrate and a larger-notch trowel, so budget for self-leveler and extra thinset. A 50 lb bag of thinset typically covers about 40 to 95 sq ft depending on trowel size.
- Rectified tile allows thinner joints. Tile with machine-squared edges can go down to 1/16 or 1/8 in; tile with pressed, slightly irregular edges usually needs 3/16 in or more.
- Plan the edges. Bullnose, trim pieces and transitions are sold separately, by the piece or linear foot.
Frequently asked questions
How much extra tile should I buy?
Add about 10 percent for a straight or offset layout, 15 percent for a diagonal layout and 20 percent for herringbone. Small rooms with many cuts, or large-format tiles where one bad cut wastes a big piece, justify a few percent more. Keep leftover tiles for future repairs.
How many tiles are in a box?
It depends on the size. Common counts are 11 to 15 pieces of 12 by 12 inch tile, 6 to 8 pieces of 12 by 24, and 3 to 5 pieces of 24 by 24. Subway tile is often sold in boxes of 40 to 80. Check the carton label or product page and enter that number.
Does the grout joint change how many tiles I need?
Slightly. Each tile plus its joint covers a bit more than the tile alone, so wider joints mean fewer tiles. With 12 by 24 inch tile and a 1/8 inch joint the difference is about 1.5 percent. With small tiles and wide joints it can be 5 to 10 percent.
How much grout do I need per square foot?
It depends on tile size, joint width and tile thickness. Large tiles with thin joints need very little: about 0.05 pounds per square foot for 12 by 24 inch tile with a 1/8 inch joint. Small mosaics with wide joints can need ten times that. The calculator works it out from the joint volume.
Should I use sanded or unsanded grout?
Use unsanded grout for joints 1/8 inch and narrower, and sanded grout for joints wider than 1/8 inch, which resists shrinking and cracking. For polished marble or glass tile that scratches easily, many installers use unsanded or a premixed urethane or epoxy grout instead.
Rates and figures last checked September 2026.
This calculator gives estimates for planning. Check current rates and product labels before you buy, list or file.