Calculate how many tiles you need for any floor or wall project. Accounts for tile size, grout gap, and waste.
Step 1: Calculate the total area to tile. Area = Length x Width
Step 2: Calculate the area of one tile including grout gap. Tile area = (tile length + grout) x (tile width + grout)
Step 3: Divide the total area by the tile area. Tiles = Area / Tile area
Step 4: Add waste factor. A 10% waste factor is standard for straight layouts. Use 15-20% for diagonal layouts or complex patterns.
Floor tiles: 12x12 in, 12x24 in, 18x18 in, 24x24 in (or 30x30 cm, 30x60 cm, 45x45 cm, 60x60 cm)
Wall tiles: 3x6 in (subway), 4x12 in, 4x16 in (or 7.5x15 cm, 10x30 cm, 10x40 cm)
Mosaic tiles: 1x1 in, 2x2 in (often sold in sheets)
Grout gap: Floor tiles typically use 1/8 in (3mm) to 3/16 in (5mm) spacers. Larger format tiles may use 1/16 in (1.5mm).
The number of tiles you need depends on the area you are tiling, the tile size, and the grout gap width. For a standard 8x10 foot bathroom floor using 12x12 inch tiles with a 1/8-inch grout gap, you need approximately 80 tiles. Add 10% for waste, and you should buy 88 tiles.
For a kitchen backsplash using 3x6 inch subway tiles, a typical area of 30 square feet requires about 240 tiles plus 10-15% waste for cuts around outlets and corners. Subway tile has more waste than larger tiles because the small size means more edge cuts.
A key detail many DIYers overlook: grout lines affect how many tiles you need. With 12x12 tiles and a 1/8-inch grout gap, the effect is small (about 2%). With smaller tiles like mosaics, grout lines become a significant percentage of the total area. Always factor grout gaps into your calculation.
Let us calculate tiles for a bathroom floor: 5 x 8 feet using 12x24 inch porcelain tiles, 1/8-inch grout gap.
Step 1: Calculate the floor area.5 x 8 = 40 square feet
Step 2: Calculate effective tile size including grout.
Tile: 12 x 24 inches. With grout: 12.125 x 24.125 inches.Effective tile area = 12.125 x 24.125 = 292.5 sq in = 2.03 sq ft
Step 3: Divide area by tile area.40 / 2.03 = 19.7 tiles
Step 4: Add waste factor (10% for a rectangular room).19.7 x 1.10 = 21.7 -- round up to 22 tiles
Step 5: Account for boxes. If tiles come in boxes of 10, buy 3 boxes (30 tiles) to ensure matching tiles from the same dye lot for future repairs.
Porcelain vs. ceramic: Porcelain tiles are denser, harder, and more water-resistant. Ideal for bathrooms, outdoor areas, and high-traffic floors. Ceramic tiles are lighter, easier to cut, and less expensive -- great for walls, backsplashes, and light-traffic floors.
Grout gap sizing: Floor tiles typically use 1/8-inch to 3/16-inch spacers. Larger format tiles (18x18 and above) can use 1/16-inch spacers. Rectified (precision-cut) tiles allow tighter joints.
Waste percentages: Straight layouts: 10%. Diagonal (45-degree): 15%. Herringbone or complex patterns: 15-20%. Small rooms with many cuts: add an extra 5%.
Do not forget grout and mortar. Thin-set mortar: one 50 lb bag covers about 60-70 sq ft for 12x12 tiles. Grout: one 25 lb bag covers about 70-90 sq ft for 12x12 tiles with 1/8-inch grout lines.
Ceramic tile: $1-$5 per sq ft. Budget-friendly, wide style selection.
Porcelain tile: $3-$10 per sq ft. More durable and water-resistant.
Natural stone (marble, travertine): $5-$25 per sq ft. Requires sealing and more maintenance.
Glass mosaic: $8-$30 per sq ft. Primarily for backsplashes and accents.
Installation: $5-$15 per sq ft professional. Setting materials add $1-$3 per sq ft.
Prices are approximate US averages for 2026 and vary by region and retailer.
| Project | Area | 12x12 Tiles | 12x24 Tiles | Est. Cost (tile only) |
|---|---|---|---|---|
| Bathroom floor | 40-60 sq ft | 44-66 | 22-33 | $80-$400 |
| Kitchen backsplash | 25-35 sq ft | n/a | 200-280 subway | $75-$350 |
| Shower walls (3-wall) | 60-90 sq ft | 66-99 | 33-50 | $180-$900 |
| Entryway / foyer | 30-50 sq ft | 33-55 | 17-28 | $90-$500 |
| Kitchen floor | 100-200 sq ft | 110-220 | 55-110 | $200-$2,000 |
Buy all tiles from the same lot number. Colors can vary between production batches. Verify lot numbers on every box before starting.
Dry-lay your tiles before setting them. Place tiles without mortar to check the layout and avoid narrow slivers at walls.
Never use mastic in wet areas. Showers and tub surrounds require thin-set mortar. Mastic is only for dry-area wall tile like backsplashes.
Large-format tiles need flat substrates. Uneven floors cause large tiles to rock and crack. Use self-leveling compound first.
Keep spare tiles. Store at least 5-10% extra from the same lot for future repairs. Matching tiles years later is often impossible.
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