How the calculator works
Enter the area, or its length and width, then the tile size, the grout joint and the tile thickness.
- Area: length × width. For an L-shaped room, split it into rectangles and add them, or enter the total with "I know the area".
- Tile footprint: (width + joint) × (length + joint) ÷ 144 = square feet each tile covers with its share of the joint.
- Tiles: area ÷ footprint, plus the waste percentage, rounded up. Straight layouts default to 10% and diagonal or herringbone to 15%.
- Boxes: area with waste ÷ the square feet per box, rounded up.
- Grout: joint length per square foot (144 × (1 ÷ tile width + 1 ÷ tile length)) × joint width × tile thickness gives the volume; at about 0.064 pounds of sanded grout per cubic inch, plus 10%, that is the grout to buy. The factor matches a major brand's 25-pound bag coverage chart within a few percent.
Tile chart: tiles for common rooms
With 1/8-inch joints and 10% extra for cuts.
| Room | 12 × 12 in | 12 × 24 in | 3 × 6 in subway |
|---|---|---|---|
| 5 × 8 ft (40 sq ft) | 44 | 22 | 332 |
| 8 × 10 ft (80 sq ft) | 87 | 44 | 663 |
| 10 × 10 ft (100 sq ft) | 108 | 55 | 828 |
| 10 × 12 ft (120 sq ft) | 130 | 65 | 994 |
| 12 × 15 ft (180 sq ft) | 194 | 98 | 1,490 |
| 15 × 20 ft (300 sq ft) | 324 | 163 | 2,483 |
Grout joint guide
| Joint | Typical use | Grout |
|---|---|---|
| 1/16 in | Rectified porcelain, glass mosaics | Unsanded |
| 1/8 in | Most wall tile and rectified floor tile | Sanded or unsanded |
| 3/16 in | Most floor tile | Sanded |
| 1/4 in | Handmade, rustic or uneven tile | Sanded |
| 3/8 in | Saltillo, stone, wide-joint looks | Sanded |
Example: a bathroom floor in 12 × 24 tile
The bathroom is 7 ½ × 9 feet, but a 2 ½ × 5-foot tub takes up one end. The tile is 12 × 24 × 3/8 inches, laid straight with 1/8-inch joints, and a box covers 15.5 square feet.
- Area: 7.5 × 9 = 67.5 square feet, less 2.5 × 5 = 12.5 for the tub, leaves 55 square feet.
- Footprint: 12.125 × 24.125 ÷ 144 = 2.03 square feet per tile.
- Tiles: 55 ÷ 2.03 = 27.1 tiles; with 10% extra, 29.8, so 30 tiles.
- Boxes: 55 × 1.1 = 60.5 square feet ÷ 15.5 = 3.9, so 4 boxes.
- Grout: about 3.2 pounds of sanded grout, so a 10-pound bag or a small box is plenty.
Tips
- Start from the center. Snap chalk lines through the middle of the room and dry-lay a row each way, so the cut tiles at the walls are even and not thin slivers.
- Check tiles from every box. Shuffle tiles from several boxes as you lay them to blend small color differences.
- Use the right trowel. Large tiles need a bigger notch and back-buttering for full coverage; the thinset bag lists the trowel for each tile size.
- Leave the joint at walls. Leave a ¼-inch gap at walls and fixtures for movement, hidden later by baseboard or caulk.
- Count the trim. Bullnose, edge trim and cove base are sold by the piece or linear foot, so measure them separately.
Frequently asked questions
How many tiles do I need for 100 square feet?
With 1/8-inch grout joints, 100 square feet takes about 98 tiles of 12 × 12 inches, 49 of 12 × 24 inches or 25 of 24 × 24 inches. Add 10% for cuts on a straight layout, which makes 108, 55 and 28 tiles. Small tiles add up fast; 100 square feet of 3 × 6 subway tile is about 752 tiles before waste.
How much extra tile should I buy?
About 10% for a straight or offset layout, and 15% or more for diagonal, herringbone or a room with many corners. Buy the extra from the same lot at the same time, because colors can vary between production runs, and keep a few spare tiles for future repairs.
How do I calculate tiles per square foot?
Divide 144 by the tile's width plus the joint times its length plus the joint, all in inches. A 12 × 24-inch tile with 1/8-inch joints covers 12.125 × 24.125 = 292.5 square inches, so 144 ÷ 292.5 = 0.49 tiles per square foot.
How much grout do I need?
It depends on the tile size, joint width and tile thickness. Using a leading brand's coverage chart, a 25-pound bag of sanded grout fills about 350 square feet of 12 × 12 × 3/8-inch tile with 1/8-inch joints, but only about 120 square feet with 3/8-inch joints. The calculator works it out and adds 10%; check the bag's own chart.
How many boxes of tile do I need?
Divide the area including waste by the square feet each box covers, printed on the box, and round up. 120 square feet plus 10% is 132 square feet; with boxes of 16 square feet that is 8.25, so buy 9 boxes.
What size grout joint should I use?
1/16 to 1/8 inch for rectified tile with straight, precise edges, 1/8 to 3/16 inch for most floor and wall tile, and 1/4 inch or more for handmade or rustic tile with uneven edges. Sanded grout is for joints of 1/8 inch and wider; narrower joints take unsanded grout. Follow the tile maker's minimum.
Last updated October 21, 2026.