How to use the tile calculator
- Measure the floor or wall area. For a backsplash or shower, measure each wall section and add them up, then use "I know the sq ft".
- Enter the tile's nominal size in inches. Large-format tiles like 12 × 24 work fine.
- Pick the grout joint width and tile thickness to get a grout estimate.
- Choose the waste allowance. Diagonal and herringbone layouts produce more offcuts.
Tile formula
tiles = area (sq ft) × 144 ÷ ((tile width + joint) × (tile length + joint))
tiles to buy = tiles × (1 + waste %)
Grout is estimated from the total joint volume: the joint length per square foot × joint width × tile thickness, at roughly 0.065 lb of sanded grout per cubic inch. Different grouts vary, so compare with the coverage chart on the bag.
Tiles needed for common areas
| Area (sq ft) | Tile size | Tiles (no waste) | Tiles with 10% waste |
|---|---|---|---|
| 30 | 3 × 6 in | 226 | 249 |
| 40 | 12 × 12 in | 40 | 44 |
| 50 | 12 × 24 in | 25 | 28 |
| 100 | 12 × 12 in | 98 | 108 |
| 100 | 18 × 18 in | 44 | 49 |
| 100 | 12 × 24 in | 50 | 55 |
| 200 | 24 × 24 in | 50 | 55 |
Values assume 1/8 inch grout joints.
Tips before you buy
- Buy all the tile at once and check every box has the same lot or batch number. Color can shift between batches.
- Keep a few spare tiles for future repairs.
- Large tiles (15 in or more on a side) usually need a minimum 1/8 inch joint and a flatter floor, and they waste more on small rooms.
Frequently asked questions
How many 12x12 tiles do I need for 100 square feet?
About 98 tiles with 1/8 inch joints, or about 108 with 10% extra for cuts and breakage.
How much extra tile should I buy?
10% for straight layouts, 15% for diagonal or herringbone patterns, and more for rooms with many corners or very large tiles.
How much grout do I need?
For 12 × 12 tile with 1/8 inch joints, 3/8 inch thick, plan on about 0.08 lb per sq ft, so a 25 lb bag covers roughly 300 sq ft. Smaller tiles and wider joints need much more.