Core answer: Tiles needed = area ÷ tile area × (1 + waste rate). Waste: 5% for straight layouts, 8–10% for diagonal/herringbone, 10–15% for complex cuts. Example: 20 m² floor with 600×600 mm tiles (0.36 m² each), straight layout: 20 ÷ 0.36 × 1.05 = 58.3 → buy 59–60 tiles, then round UP to whole boxes (600×600 usually 4/box → 15 boxes = 60). Always buy from the same batch (色号) and keep 2–3 spares for future repairs.
The math in steps
- Measure the actual area (subtract permanent fixtures like floor cabinets for walls).
- Tile area: side × side (600×600 = 0.36 m²; 800×800 = 0.64; 750×1500 = 1.125; 300×600 wall = 0.18).
- Count = area ÷ tile area.
- Waste: ×1.05 straight / ×1.08–1.10 diagonal / ×1.10–1.15 herringbone or tiny mosaics.
- Round to boxes, not pieces.
Quick reference: pieces per m²
| Size | m²/piece | pieces/m² | +10% waste |
|---|---|---|---|
| 300×300 | 0.09 | 11.1 | 12.2 |
| 300×600 | 0.18 | 5.6 | 6.1 |
| 600×600 | 0.36 | 2.78 | 3.06 |
| 800×800 | 0.64 | 1.56 | 1.72 |
| 600×1200 | 0.72 | 1.39 | 1.53 |
| 750×1500 | 1.125 | 0.89 | 0.98 |
Worked examples
Example 1 — Bathroom walls. Bathroom 4 m² floor, walls to 2.4 m height, perimeter 8.4 m: wall area = 8.4 × 2.4 − door 1.7 m² ≈ 18.5 m². 300×600 tiles: 18.5 ÷ 0.18 × 1.08 = 111 → boxes of 8 → 14 boxes (112 pieces).
Example 2 — Living room with diagonal. 30 m², 800×800 diagonal layout: 30 ÷ 0.64 × 1.10 = 51.6 → 52 pieces; boxes of 3 → 18 boxes (54). The diagonal pattern costs ~5 extra tiles on 30 m² — beauty has a waste rate.
Example 3 — The batch problem. Ordered 55, ran short 3 tiles; reordered — new batch has a visible shade difference (色差). Tiles are fired in batches; the SAME model from a different batch can mismatch. Solution: order full quantity +3 spares in ONE order, verify 色号/批号 on every box at delivery.
Example 4 — Skirting/波导线. Border strips counted in LINEAR meters, not area: 30 m² room perimeter ~22 m; 800×100 skirting pieces: 22 ÷ 0.8 × 1.05 = 29 pieces.
Common mistakes and myths
- Forgetting waste entirely — ordering exact area guarantees a mid-job shortage; cuts, breakage, and future repairs are certain.
- Not rounding to boxes — tiles sell by the box; 59 pieces needed = 15 boxes of 4 = 60, not 59.
- Mixing batches — always inspect box labels for 色号/批号 at delivery; refuse mixed batches for the same room.
- Ignoring the layout decision — diagonal/herringbone changes waste from 5% to 10%+; decide the pattern BEFORE ordering.
- Returning leftovers late — most sellers accept unopened full-box returns within 1–2 weeks; agree the return terms at purchase, keep boxes dry.