How to use the tile calculator
Enter the size of the floor or wall, choose the tile and the grout joint, and the calculator counts tiles with your waste allowance. It also estimates sanded grout from the actual joint volume (joint width × tile thickness × total joint length) and thinset from the trowel you'll use. The layout drawing shows your tile and joint at true proportion.
The grout formula was checked against CUSTOM Building Products' published Polyblend coverage chart. Across the chart's tile and joint sizes it lands within roughly 10 to 20 percent, so round up to the next bag.
The formulas
tiles per ft² = 144 ÷ ((tile length + joint) × (tile width + joint))
tiles = area × tiles per ft² × (1 + waste)
grout (in³ per ft²) = joint × thickness × (L + W + joint) ÷ ((L + joint)(W + joint)) × 144
grout (lb) = in³ × 0.064
Worked example: 100 ft² of 12 × 12 in tile, ⅛ in joints
- Each tile with its joint takes 12⅛ × 12⅛ = 147 in², so 0.98 tiles per ft².
- Tiles: 100 × 0.98 = 98, plus 10% = 108 tiles.
- Grout: ⅛ × ⅜ × 24⅛ ÷ 147 × 144 × 100 = 111 in³ of joint, about 7 lb: one 25 lb bag with plenty to spare.
- Thinset with a ¼ × ⅜ in trowel at 60 ft² per bag: 2 bags.
Grout per 100 ft² (sanded, ⅜ in thick tile)
| Tile | ⅛ in joint | ¼ in joint |
|---|---|---|
| 12 × 12 in | 7 lb | 14 lb |
| 12 × 24 in | 5 lb | 11 lb |
| 18 × 18 in | 5 lb | 9 lb |
| 6 × 24 in | 9 lb | 17 lb |
Tips
- Sanded or unsanded? Sanded grout for joints ⅛ in and wider; unsanded for joints narrower than ⅛ in and for easily scratched stone or glass. Check the grout's own range.
- Lay it out dry first. Center the layout so cut tiles at the walls are at least half a tile.
- Large tiles need a flat floor and often a leveling system. Lippage (uneven edges) shows on big tiles.
- Same lot. Check that every box has the same shade and lot number before you start.
Questions people ask
How many tiles do I need for 100 square feet?
With 12 × 12 in tiles and ⅛ in joints, about 98 tiles before waste, or 108 with 10% extra. Each tile plus its share of the joint covers a little more than a square foot. For 12 × 24 in tiles it's about 50, or 55 with waste.
How much grout do I need?
It depends on joint width and tile size more than on area. 100 square feet of 12 × 12 × ⅜ in tile with ⅛ in joints takes about 7 lb of sanded grout; with ¼ in joints about 14 lb. Small mosaics take far more: 1 in mosaics with ⅛ in joints use around 46 to 48 lb per 100 square feet.
How much extra tile should I buy?
10% for straight layouts in a simple room, 15% for diagonal or herringbone layouts and rooms with lots of cuts. Keep a box or two for future repairs, since dye lots change.
How much thinset do I need?
CUSTOM's VersaBond data sheet gives 85 to 95 square feet per 50 lb bag with a ¼ × ¼ in square-notch trowel and 60 to 67 with a ¼ × ⅜ in trowel. Bigger tiles need bigger notches and more mortar.
What size trowel should I use for tile?
As a rough guide: ¼ × ¼ in square notch for tiles up to about 8 in, ¼ × ⅜ in for 12 in tiles, and ½ × ½ in for large-format tiles. Always check coverage by lifting a tile: at least 80% contact in dry areas and 95% in wet areas.
Sources and assumptions
- CUSTOM Building Products Polyblend Sanded Grout data sheet: coverage chart per 25 lb bag (used to calibrate the grout formula to 0.064 lb per in³ of joint)
- CUSTOM VersaBond Professional Thin-Set Mortar (TDS-119): 85-95 ft² per 50 lb bag (¼ × ¼ in notch), 60-67 ft² (¼ × ⅜ in notch); 80% / 95% coverage requirements
- Grout volume = joint width × tile thickness × joint length. Results land within about 10-20% of the manufacturer's chart; buy the next bag up.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.