Measuring floors and walls
- Floors: measure wall to wall at the widest points. Measure closets and alcoves as separate rectangles and add them together. Leave out areas under fixed cabinets and tubs.
- Walls and backsplashes: measure the width and height of each wall section, and subtract windows and large openings. For a backsplash, measure only the area between the counter and the upper cabinets.
- Showers: each wall is its own rectangle. Add the floor and any niches separately, often with different tile.
For an L-shaped room, calculate each rectangle with the calculator, or add the areas and enter the total as length × 1 ft.
Why grout width matters
Each tile takes up its own size plus one grout joint in each direction. Tiles needed = area ÷ ((tile length + joint) × (tile width + joint)), then waste is added. For 12 in tile with ¼ in joints, each tile occupies 12.25 × 12.25 in = 1.042 ft². A 20 × 15 ft floor (300 ft²) therefore needs 288 tiles before waste, slightly fewer than 300. The effect is bigger with small tile: 2 × 2 in mosaics with ⅛ in joints lose more than 10% of their area to grout.
Tiles per 100 ft² by sizeTiles per 10 m² by size
| Tile size | Joint | Tiles per 100 ft² (no waste) | With 10% waste | With 15% waste |
|---|---|---|---|---|
| 3 × 6 in | 0.125 in | 753 | 828 | 866 |
| 4 × 4 in | 0.125 in | 847 | 931 | 974 |
| 6 × 6 in | 0.125 in | 384 | 423 | 442 |
| 12 × 12 in | 0.125 in | 98 | 108 | 113 |
| 12 × 24 in | 0.125 in | 50 | 55 | 57 |
| 18 × 18 in | 0.1875 in | 44 | 48 | 51 |
| 24 × 24 in | 0.1875 in | 25 | 28 | 29 |
| 6 × 36 in | 0.125 in | 66 | 72 | 75 |
| Tile size | Joint | Tiles per 10 m² (no waste) | With 10% waste | With 15% waste |
|---|---|---|---|---|
| 7.5 × 15 cm | 3 mm | 838 | 922 | 964 |
| 10 × 10 cm | 3 mm | 943 | 1,037 | 1,084 |
| 15 × 15 cm | 3 mm | 428 | 470 | 492 |
| 20 × 20 cm | 3 mm | 243 | 267 | 280 |
| 30 × 30 cm | 3 mm | 109 | 120 | 126 |
| 30 × 60 cm | 3 mm | 55 | 61 | 63 |
| 45 × 45 cm | 5 mm | 49 | 54 | 56 |
| 60 × 60 cm | 5 mm | 28 | 31 | 32 |
| 15 × 90 cm | 3 mm | 73 | 80 | 84 |
How much extra tile to order
The TCNA Handbook covers installation methods but doesn't prescribe a single waste percentage. The figure depends on the layout and the room. Industry guidance commonly suggests about 10% for a straight lay, 15% for a 45° diagonal, and around 20% for herringbone or chevron. Add more for small rooms with many cuts, or for natural stone with colour variation. Separately, keep at least one unopened box as attic stock for future repairs, because tile lots change and colours rarely match later.
Boxes and lots
Tile is sold by the box, either as a count of pieces or as square feet per box. If the box lists square feet, divide your area with waste by that figure instead. Check that every box has the same lot (shade) number before you leave the store. Mixing lots can create visible patches. Open a few boxes and blend tiles as you lay them.
Worked examples
Bathroom floor, 8 × 5 ft, 12 × 24 in tile, ⅛ in jointBathroom floor, 2.44 × 1.52 m, 30.5 × 61 cm tile, 3.2 mm joint
Area length 8 ft · Area width 5 ft · Tile length 24 in · Tile width 12 in · Grout joint 0.125 in · The box label gives Tiles per box · Tiles per box 8 · Box covers 12 ft² · Waste / overage 15 %Area length 2.44 m · Area width 1.52 m · Tile length 61 cm · Tile width 30.5 cm · Grout joint 3.2 mm · The box label gives Tiles per box · Tiles per box 8 · Box covers 1.11 m² · Waste / overage 15 %
- Tiles needed (with waste): 23
- Tiles before waste: 20
- Boxes: 3
Kitchen backsplash, 14 ft × 18 in, 3 × 6 in subway, ⅛ in jointKitchen backsplash, 4.27 m × 45.7 cm, 7.6 × 15.2 cm subway, 3.2 mm joint
Area length 14 ft · Area width 1.5 ft · Tile length 6 in · Tile width 3 in · Grout joint 0.125 in · The box label gives Tiles per box · Tiles per box 80 · Box covers 12 ft² · Waste / overage 10 %Area length 4.27 m · Area width 0.46 m · Tile length 15.2 cm · Tile width 7.6 cm · Grout joint 3.2 mm · The box label gives Tiles per box · Tiles per box 80 · Box covers 1.11 m² · Waste / overage 10 %
- Tiles needed (with waste): 174
- Boxes: 3
Living room, 20 × 15 ft, 12 × 12 in, ¼ in joint, diagonalLiving room, 6.1 × 4.57 m, 30.5 × 30.5 cm, 6.3 mm joint, diagonal
Area length 20 ft · Area width 15 ft · Tile length 12 in · Tile width 12 in · Grout joint 0.25 in · The box label gives Tiles per box · Tiles per box 12 · Box covers 12 ft² · Waste / overage 15 %Area length 6.1 m · Area width 4.57 m · Tile length 30.5 cm · Tile width 30.5 cm · Grout joint 6.4 mm · The box label gives Tiles per box · Tiles per box 12 · Box covers 1.11 m² · Waste / overage 15 %
- Tiles needed (with waste): 332
- Tiles before waste: 288
- Boxes: 28
Thinset, grout and backer
Thinset and grout coverage depends on the tile size, the trowel notch and the joint width and depth, so each manufacturer publishes its own coverage chart. Use the chart for your product rather than a generic rule. Showers and wet areas need a suitable backer and waterproofing. Regular drywall isn't a substitute. Large or heavy tiles may need larger trowel notches or back-buttering to get full coverage, so follow the tile and mortar makers' instructions.
Common mistakes
- Ignoring the grout joint, which slightly overstates the count for small tiles.
- Ordering 10% for a diagonal layout. Diagonals cut more tiles at every edge.
- Forgetting bullnose or trim pieces for wall edges and outside corners. They're sold separately, by linear foot.
- No attic stock. A cracked tile years later is easy to fix if you have spares.
Plan the layout before you buy
Snap center lines in both directions and dry-lay a row of tile along each one. You want the cut pieces at opposite walls to be roughly equal, and not thin slivers. If a line of tile leaves a sliver at one wall, shift the starting line by half a tile. A dry layout also shows where the tile will meet doorways, tubs and cabinets, and where the most visible full tiles should go. It doesn't change the count much, but a layout with many small cuts uses more of your waste allowance, so go toward the top of the range in that case.
Checked against
Each case below is re-run against the calculator by our automated test suite.
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 20 × 15 ft, 12 in tiles, ¼ in grout, before waste | 288 | calculator.net tile calculator | Match |
| Same floor with 10% waste | 317 | calculator.net tile calculator | Match (top of its 303–317 range) |
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 6.1 × 4.57 m, 30.5 cm tiles, 6.3 mm grout, before waste | 288 | calculator.net tile calculator | Match |
| Same floor with 10% waste | 317 | calculator.net tile calculator | Match (top of its 303–317 range) |
Frequently asked questions
How many 12 × 12 tiles for 300 ft²?
With ¼ in grout, 288 tiles before waste, or 317 with 10%.
How many tiles do I need for a 10 × 10 room?
With 12 in tile and ⅛ in joints, about 98 tiles before waste, or 108 with 10%.
How much extra tile should I buy?
About 10% for straight layouts, 15% for diagonal and around 20% for herringbone, plus a spare box for repairs.
Does grout width change the tile count?
Yes. Each tile covers its size plus one joint, so wider joints mean slightly fewer tiles. The effect is largest with small tile.
Sources & assumptions
The results are planning estimates, and the cost figures only use prices you enter. Product yields, densities and coverage rates vary, so check the label or ask your supplier, and follow local codes. Figures marked "approximate" or "rule of thumb" are general practice, not exact standards.
See how we calculate and test our formulas and the changelog. Last updated 2026-10-08.
Reviewed by the MaterialWhiz Editorial Team. This estimate uses the assumptions shown in the calculator. Review the result against your supplier's product coverage and site conditions. Last reviewed: October 10, 2026. See how we calculate · Report a correction.