The Basic Tile Formula
Formula:
(Room Area ÷ Tile Area) × Waste Factor = Tiles Needed
Waste factor: 1.10 for straight lay, 1.15 for diagonal, 1.20 for complex patterns
Step-by-Step Guide
Step 1: Measure the Room Area
Measure the length and width of the floor or wall in metres (or feet). Multiply them together to get the total area.
Step 2: Find Your Tile Area
Check the tile dimensions (usually on the box). Multiply length × width to get the area of one tile.
Common tile sizes and their area:
| Tile Size | Area per tile |
|---|---|
| 300×300mm | 0.09 m² |
| 600×300mm | 0.18 m² |
| 600×600mm | 0.36 m² |
| 900×600mm | 0.54 m² |
| 1200×600mm | 0.72 m² |
Step 3: Add Waste Percentage
Always order extra tiles to account for cuts, breakage, and future repairs. The amount depends on your layout:
Straight / Grid lay
Most common, minimal cuts
Brick / Offset pattern
Slightly more cuts at edges
Diagonal / 45° lay
Many corner cuts needed
Herringbone pattern
Complex cuts throughout
Step 4: Calculate Total Tiles
Worked Example:
- Room: 4m × 5m = 20 m²
- Tile: 600×600mm = 0.36 m² per tile
- Base count: 20 ÷ 0.36 = 55.6 → 56 tiles
- + 10% waste: 56 × 1.10 = 61.6 → order 62 tiles
Special Situations
Bathrooms & Wet Areas
For bathrooms, calculate walls and floor separately. Remember to subtract the bath/shower tray area from the floor, and door openings from the walls.
L-Shaped Rooms
Break the room into rectangles, calculate each area separately, then add them together before applying the waste factor.
Feature Walls
For a single feature wall, multiply height × width and add 10–15% waste. If using a different pattern like herringbone, use 20% waste.
Don't Forget Grout
A general rule: for 2–3mm grout joints, you'll need approximately 1kg of grout per 5 m² of 300×300mm tiles. Larger tiles need less grout, smaller mosaic tiles need more.
Top Tips
Always buy 10% extra — tile batches vary in colour and discontinued tiles are hard to match later
Start tiling from the centre of the room outwards for a balanced look
Use a laser level or chalk line to keep your first row perfectly straight
Store leftover tiles flat in a cool, dry place for future repairs