Running out of tiles mid-project is one of the most avoidable and frustrating DIY mistakes. You stop work, the batch is discontinued, or the new delivery doesn't match. The fix: calculate correctly before you buy.

This guide covers every variable — room area, tile size, grout joints, waste allowance and pattern type — so you order exactly the right amount the first time.

What You Need Before You Start

Gather these details before calculating:

From the tile packaging

  • Tile dimensions: length × width (e.g. 600 × 300 mm or 24" × 12")
  • Tiles per box: how many tiles are in one carton
  • Coverage per box: often printed as m² or ft² — use this if available
  • Recommended grout joint width: usually 2–5 mm for floor tiles, 1.5–3 mm for wall tiles

From the room

  • Total area to be tiled (floor, wall, or both)
  • Obstacles to subtract: bath tub, shower tray, kitchen island — only subtract large fixed items you are certain will not move
  • Number of cuts: more corners, niches and pipes = more waste
Pro TipIf the box shows coverage per carton (e.g. 1.08 m²), use that directly — you don't need to calculate individual tile area unless you're double-checking the supplier's numbers.

Step 1 — Measure Your Area

Simple rectangular rooms

Area = length × width

Metric example: 3.2 m × 2.8 m = 8.96 m²

Imperial example: 10.5 ft × 9 ft = 94.5 ft²

L-shaped rooms and irregular spaces

Divide the space into rectangles, calculate each separately and add them together. This approach also helps you plan tile layout for each zone independently.

  • Zone A: 3.0 m × 2.0 m = 6 m²
  • Zone B: 1.5 m × 1.2 m = 1.8 m²
  • Total: 6 + 1.8 = 7.8 m²

Wall tiling

For each wall: width × height. Subtract windows and doors if they are large — but keep small sections like the area above a window unless it is more than 0.5 m².

Don't under-subtractOnly deduct areas you are 100% certain are fixed and permanent — like a built-in bath. A door opening or radiator alcove should be kept in the total. Tiles cut for those areas often get used as infill elsewhere.

Step 2 — Calculate How Many Tiles

Tile area (if not printed on the box)

Tile area (m²) = (tile length in m) × (tile width in m)

Example: 600 mm × 300 mm = 0.60 m × 0.30 m = 0.18 m² per tile

Tile area (ft²) = (length in inches × width in inches) ÷ 144

Example: 24" × 12" ÷ 144 = 2.0 ft² per tile

Raw tile count (before waste)

Tiles needed = total area ÷ area per tile

Example: 8.96 m² ÷ 0.18 m² = 49.8 → round up to 50 tiles

Skip the manual math — use the tile calculator

Enter your room dimensions and tile size. Get an instant tile count, box count and cost estimate in metric or imperial.

Open Tile Calculator

Step 3 — Add Waste Allowance

No room tiles perfectly without cuts. Every cut produces off-cuts, and some break during installation. Use these benchmarks:

Situation Waste %
Simple rectangular room, straight lay, large tiles 5–7%
Standard room with a few cuts (doors, alcoves) 8–10%
Complex room, many obstacles, smaller tiles 10–15%
Diagonal or herringbone pattern 15–20%
Natural stone with pattern matching 20%+

Tiles with waste = raw count × (1 + waste %)

Example: 50 tiles × 1.10 = 55 → round up to 55 tiles

Always buy from the same batchTiles are produced in batches. Even the same product code can have slight colour or texture variation between batches. Order everything in one go and check that all boxes share the same batch number.

Step 4 — Account for Grout Joints

Grout joints take space. For large-format tiles (600 mm+), this has minimal impact. For smaller mosaic or subway tiles, grout can noticeably affect how many full tiles fit across a row.

Effective tile size (with grout)

Effective tile length = tile length + grout joint width

Example: 300 mm tile + 3 mm joint = 303 mm effective size

Use the effective tile size when planning layout and confirming that full tiles fit without awkward slivers at the edges.

Avoid thin sliversIf your layout leaves less than half a tile at the edge, shift the starting point so you get equal cuts on both sides. This looks far more professional and is actually easier to install.

Patterns: Offset, Diagonal & Herringbone

Straight lay (grid pattern)

Tiles align in rows and columns, joints lined up. Most efficient layout — minimum waste. Standard choice for large floors and walls.

Offset (brick bond / running bond)

Each row is shifted by half a tile length (or one-third). Very common for subway tiles and rectangular tiles. Waste: 8–10%. Works well for hiding subfloor unevenness.

Diagonal (45°)

Tiles are rotated 45° to the walls. More cuts at every perimeter wall and around all obstacles. Makes a room feel wider. Waste: 15–20%. Requires careful planning to keep diagonal lines even.

Herringbone and chevron

Tiles are set in a V-shaped zigzag pattern. Requires many more cuts, especially at borders. Best suited to rectangular tiles (2:1 or 3:1 ratio). Waste: 15–20%, sometimes more in small spaces or around fixtures.

Dry-lay before you fixFor herringbone or diagonal, always lay out a section without adhesive first. Confirm the pattern looks right, check edge cuts and make sure grout lines align before committing.

Wall Tiles vs. Floor Tiles

The calculation method is identical, but a few things differ:

  • Wall tiles are typically lighter and thinner — do not use wall tiles on floors, they will crack under foot traffic
  • Gravity affects layout: plan where you want full tiles to show (eye level, focal walls) and where cut tiles can hide (behind toilets, in corners)
  • Fixtures break rows: taps, switches and soap holders all require precise cuts — add at least 5% extra for complex bathrooms with many fittings
  • Measure height carefully: ceiling heights vary — always measure at the highest point of each wall

6 Mistakes That Lead to Re-Ordering

1. Measuring only the easy walls

Most people measure length and width and forget alcoves, chimney breasts and bay windows. Measure every section separately.

2. Skipping waste allowance

A calculation with zero waste assumes perfect tiles and no cuts. Even professional tilers use at least 5%.

3. Forgetting grout when planning layout

Grout joints push tiles apart. Ignoring this leads to unexpected slivers at the end of a row.

4. Mixing batches mid-project

Tiles from different production batches can look noticeably different in certain lighting. Always buy all tiles in one order from one batch.

5. Not ordering spare tiles

Even after a successful installation, keep 5–10 spare tiles. Matching a discontinued tile 3 years later is almost impossible.

6. Using floor tile quantities for wall tiles (or vice versa)

If you are tiling both floor and walls, calculate them separately. Tile sizes, grout widths and waste percentages often differ between the two surfaces.

Quick Reference Summary

Step Formula
Room area length × width
Tile area tile length × tile width (in same unit)
Raw tile count room area ÷ tile area → round up
With waste raw count × (1 + waste %) → round up
Boxes needed total tiles ÷ tiles per box → round up

Ready to get your exact tile count? Use our tile calculator — enter your room size, tile dimensions and pattern type for instant results in metric or imperial.