Buying tiles for a flooring or wall project sounds simple until you realize that running out halfway through installation is a nightmare — and buying too many means wasting hundreds of dollars. The difference between a smooth project and a stressful one often comes down to one thing: accurate measurement and calculation. In this guide, we will show you exactly how to measure any room for tiles, calculate the precise number you need, add the correct waste margin, and avoid the most common mistakes homeowners make.
Step 1: Measure the Room Accurately
Before you touch a calculator, you need reliable measurements. Use a quality tape measure — ideally a laser measure for large rooms — and record the length and width of the space in the same unit system you plan to use for your tiles. Most tile calculators accept either metric (meters and centimeters) or imperial (feet and inches).
Important: Measure wall-to-wall at the widest points. Do not assume walls are perfectly straight, especially in older homes. Measure at the floor level, not at waist height, as walls can bow outward or inward.
- Measure the length and width of the room.
- For L-shaped rooms, divide the space into rectangles and measure each separately.
- Subtract the area of fixed objects (kitchen islands, bathtubs, built-in cabinets) if they will not be tiled underneath.
- Do not forget closets, alcoves, and entryways — these add significant area.
Step 2: Know Your Tile Size
Tile sizes vary dramatically, and the size you choose affects how many you need. Common sizes include:
| Tile Size | Typical Use | Area per Tile |
|---|---|---|
| 30×30 cm | Small bathrooms, mosaics | 900 cm² (0.09 m²) |
| 60×60 cm | Standard floors, living rooms | 3,600 cm² (0.36 m²) |
| 80×80 cm | Large open spaces | 6,400 cm² (0.64 m²) |
| 30×60 cm | Walls, subway layouts | 1,800 cm² (0.18 m²) |
Larger tiles cover more area per piece, which means fewer total tiles. However, larger tiles also generate more waste when cutting around corners, pipes, and irregular edges.
Step 3: Calculate Base Tile Count
For a room measuring 5 meters by 4 meters (20 m² total) using 60×60 cm tiles (0.36 m² each):
20 m² ÷ 0.36 m² = 55.55 tiles → round up to 56 tiles
Always round up. You cannot buy 0.55 of a tile, and rounding down guarantees a shortage.
Step 4: Add the Waste Margin
This is where most DIYers make mistakes. Cutting tiles to fit edges, corners, and fixtures always produces waste. Broken tiles during transport or installation are also common. The waste percentage depends on your layout complexity:
- 5% waste: Perfectly square room, straight grid layout, no obstacles.
- 10% waste: Standard room with a few corners and one doorway. (Recommended default)
- 15% waste: Diagonal or herringbone pattern, multiple cutouts.
- 20% waste: Complex room with pillars, curved walls, or many fixtures.
For our 20 m² room with a standard 10% waste margin: 56 tiles × 1.10 = 61.6 → 62 tiles.
Step 5: Convert to Boxes
Tiles are sold in boxes, not individually. A typical box contains 4 to 10 tiles depending on size. Check the box label for the exact count and total coverage area. Divide your total tile count by tiles per box, and round up again.
62 tiles ÷ 6 tiles per box = 10.33 → buy 11 boxes
Pro Tips from Contractors
💡 Buy extra boxes for repairs
Keep 1–2 unopened boxes after installation. Tile dye lots change over time, and matching a broken tile two years later is nearly impossible.
💡 Check the dye lot number
Tiles from different production batches can have slight color variations. Buy all boxes from the same lot number.
💡 Dry lay before you glue
Lay out a few rows without adhesive first to check spacing, pattern alignment, and edge cuts.
Use Our Free Tile Calculator
Skip the manual math and use our free Tile & Flooring Calculator. Enter your room dimensions, tile size, and waste percentage, and get instant results for total area, exact tile count, and tiles with waste margin included.
Written by Alex Morgan. Last updated August 2026.