How to calculate tile quantity

The complete formula — from room area to tiles in your shopping cart

The basic formula

At its simplest, the number of tiles you need is the room area divided by the area of one tile (including its share of the grout gap), multiplied by a waste factor. But getting this right requires understanding each variable.

Step 1: Calculate the room area

For a rectangular room, multiply width by length. A room that measures 300 cm by 250 cm has an area of 75,000 cm² or 7.5 m². For irregular shapes, break the room into rectangles, calculate each area separately, and add them together.

Step 2: Calculate the tile pitch

The "pitch" is the centre-to-centre distance between tiles — the tile dimension plus the grout gap. A 30 cm tile with a 2 mm grout gap has a pitch of 30.2 cm. The area covered by one tile at its pitch is 30.2 × 30.2 = 912.04 cm².

This matters because grout gaps eat into the room area. Using just the tile face area (30 × 30 = 900 cm²) would undercount — you'd come up short by about 1-2% on a typical room.

Step 3: Divide to get net tiles

Divide the room area by the single tile pitch area. For our example: 75,000 ÷ 912.04 = 82.2 tiles. Round up to 83 — you can't buy a fraction of a tile.

Step 4: Add pattern waste

A straight layout has near-zero pattern waste. A brick bond adds about 5%. Herringbone and diagonal patterns add 10-15%. Multiply your net tile count by the waste factor:

• Straight: × 1.00
• Brick bond: × 1.05
• Herringbone: × 1.10 to 1.15
• Diagonal: × 1.10 to 1.15

Step 5: Add cutting reserve

This covers breakages during cutting, measurement errors, and future repairs. A standard reserve is 5% for simple rectangular rooms and 10% for complex shapes or if you're a beginner.

When the simple formula isn't enough

The formula above gives a good estimate, but it doesn't tell you about the quality of the cuts. A room might need 93 tiles, but if the layout puts a 5 mm sliver against the most visible wall, the tiler will shift the grid — which might increase the total. This is where a proper layout planner earns its keep: it shows you exactly where every cut falls and lets you optimise the starting position to avoid thin strips.

Tiles per box vs total count

Tiles are sold in boxes. Once you know your total tile count, divide by the number of tiles per box and round up. Always buy complete boxes — loose tiles from returned boxes may have slight colour variation from a different production batch.