How to calculate tile for a floor or wall
Find how many tile boxes you need for any surface — with the correct waste allowance for your installation pattern.
Tile calculation comes down to three numbers: surface area, coverage per box and waste percentage. Get those right and you will order exactly what you need without running short mid-job or wasting money on excess. The waste percentage is the variable most people underestimate.
Boxes = ceil(area × (1 + waste%) ÷ coverage per box). Always round up — you cannot return half a box.
Step 1 — Measure the surface
For a rectangular floor or wall, measure length × width in meters (or feet). For an L-shaped room or one with an island or alcove, divide the space into rectangles, calculate each area separately and add them together. Measure to the finished wall — do not deduct baseboards or trim since tiles will go underneath.
For a backsplash, measure the area between worktop and upper cabinets. A typical kitchen backsplash is 0.5–1.5 m² (5–16 sq ft).
Step 2 — Find coverage per box
Coverage is printed on the box in m² or sq ft. It accounts for typical joint width. Do not calculate it yourself from tile dimensions — the manufacturer's figure is always more accurate. Standard boxes typically cover 1.5–2.5 m² (16–27 sq ft) depending on tile size.
Step 3 — Choose the right waste percentage
Waste covers edge cuts, broken tiles during installation and off-cuts that cannot be reused. Use these reference values:
| Installation pattern | Waste to add | Why |
|---|---|---|
| Straight lay (joints parallel) | 10% | Cuts only at room edges |
| Offset / brick bond (⅓ offset) | 10–12% | Slightly more edge cuts |
| Diagonal (45°) | 15–20% | All four edges require angled cuts |
| Herringbone / chevron | 15–20% | Complex angles, many small cuts |
| Room with many obstacles | +5% extra | Columns, pipes, irregular walls |
Step 4 — Calculate boxes
Apply the formula: Boxes = ceil(area × (1 + waste%) ÷ coverage per box). The ceil (ceiling) function means you always round up to the next whole box — you cannot buy a partial box.
Worked example — 4 m × 3 m bathroom floor, diagonal pattern
Area = 4 × 3 = 12 m² (129 sq ft). Box coverage = 1.5 m² (16 sq ft). Waste = 15% for diagonal. Area with waste = 12 × 1.15 = 13.8 m². Boxes = ceil(13.8 ÷ 1.5) = ceil(9.2) = 10 boxes.
With a straight lay (10% waste): 12 × 1.10 = 13.2 m² ÷ 1.5 = ceil(8.8) = 9 boxes. The pattern choice costs you one extra box here.
Adhesive and grout estimates
Tile adhesive (thinset mortar): typically 3–5 kg/m² for floor tiles using a 6 mm notched trowel and back-buttering. A 25 kg bag covers approximately 5–8 m². For wall tiles with a smaller notch (4 mm), allow 2–3 kg/m².
Grout: depends on joint width and tile size. For a 30×30 cm tile with 3 mm joints, about 0.8 kg/m² of unsanded grout. For 60×60 cm tiles with 2 mm joints: about 0.3 kg/m². Always consult the grout manufacturer's technical data sheet.
Common mistakes
- Buying from different production lots. Tile color varies between production batches. Always buy all boxes at once from the same lot number printed on the box.
- Not checking surface flatness before ordering. Large-format tiles (60 cm+) require a flatter substrate. Check that variation does not exceed 3 mm over 3 m using a straightedge.
- Using 10% waste for diagonal patterns. Diagonal installations waste 15–20%. This is one of the most common ordering errors.
- Forgetting to buy spare tiles. Always order 5–10% extra and store them. Production lots change — replacing a cracked tile years later is often impossible.
Use the free calculator
Enter your area and box coverage in the Tile Calculator to get an instant box count. For paint and flooring on the same renovation, use the Paint Calculator and Laminate Flooring Calculator.
Frequently asked questions
How many tiles do I need for 100 square feet?
It depends on tile size. For 12×12 in tiles (1 sq ft each): 100 + 10% waste = 110 tiles. For 18×18 in tiles (2.25 sq ft each): about 50 tiles with waste. For 24×24 in tiles (4 sq ft): about 28 tiles with waste. Use the coverage per box from the product label.
What waste percentage for diagonal tiles?
15–20% for a diagonal (45°) or herringbone pattern. The angled cuts at every wall edge generate significantly more waste than straight-lay installations. Use 15% for experienced installers and 20% for DIY work or complex rooms.
How do I calculate tile for a backsplash?
Measure the backsplash length × height in m² or sq ft. A standard kitchen backsplash is 0.5–1.5 m² (5–16 sq ft). Apply the same formula with 10% waste for straight subway tile and 15% for herringbone or offset patterns.
Should I buy extra tiles for future repairs?
Yes — always. Buy 10–15% more than you calculate and store them. Production lot numbers change every run, and matching your original tile 3–5 years later is often impossible. The cost of a few extra boxes is trivial compared to a mismatched repair.
How much thinset adhesive do I need?
Typically 3–5 kg/m² for floors using a 6 mm notched trowel. A 25 kg bag covers about 5–8 m². For walls with a 4 mm notch: 2–3 kg/m². Always check the thinset manufacturer's coverage data for your specific product and tile size.
This guide is for preliminary planning only. Wet areas require waterproofing membranes and appropriate adhesive classes. Always follow manufacturer specifications and local building codes.