Ordering too few tiles mid-project means delays, mismatched batches, and extra costs. Ordering too many – wastes money. This guide gives you a precise, step-by-step method for calculating exactly how many bathroom tiles to order – walls, floors, and awkward spaces included.
The Core Formula for Tile Calculation
Divide the total surface area in metres squared by the area of a single tile, then add your waste allowance percentage.
That is the complete calculation. Everything else in this guide is about measuring accurately and applying the right waste percentage for your specific layout and tile size.
The formula written out:
Total tiles needed = (Surface area ÷ Single tile area) × Waste multiplier
Work in metres throughout. Mixing millimetres and metres is the most common cause of ordering errors.
Step 1: Measure Your Floor Area
Measure floor length multiplied by floor width in metres to get your base floor area before applying any waste allowance.
For a rectangular bathroom floor:
- Measure the longest length of the room in metres
- Measure the widest width of the room in metres
- Multiply the two figures together
Example: A bathroom measuring 2.4 m × 1.8 m = 4.32 m²
Irregular or L-Shaped Floors
- Split the floor into two rectangles
- Calculate each rectangle separately
- Add the two areas together for the total floor area
- Do not subtract for the toilet or basin pedestal – these are minor deductions and tiles will still be cut to fit around them
Step 2: Measure Your Wall Areas
Measure each wall individually – height multiplied by width – then subtract doors, windows, and any surfaces you are not tiling.
Do not assume all walls are the same height. Measure each one.
For Each Wall:
- Measure full height from floor to ceiling (or tiling height if not going full height)
- Measure full width including any door or window reveals
- Multiply height × width to get gross wall area
- Subtract door area (typically 2.0 m × 0.77 m = 1.54 m²)
- Subtract window area if applicable
Example wall calculation:
- Back wall: 2.4 m high × 2.4 m wide = 5.76 m²
- Side wall with door: (2.4 m × 1.8 m) − 1.54 m² = 2.78 m²
- Add all wall areas together for total wall surface
Tiling Partial Walls
Many UK bathrooms tile walls to 1.2 m or 1.8 m rather than full ceiling height. Use the actual tiling height – not the ceiling height – in your calculation. This is where most underestimates happen.
Step 3: Calculate the Area of a Single Tile
Convert your tile dimensions from millimetres to metres, then multiply length by width to find the area of one tile.
Tile sizes are sold in millimetres. Your room measurements are in metres. Convert before calculating.
Conversion Examples:
- 300 mm × 300 mm tile = 0.3 m × 0.3 m = 0.09 m² per tile
- 300 mm × 600 mm tile = 0.3 m × 0.6 m = 0.18 m² per tile
- 600 mm × 600 mm tile = 0.6 m × 0.6 m = 0.36 m² per tile
- 600 mm × 1200 mm tile = 0.6 m × 1.2 m = 0.72 m² per tile
Most tile retailers list coverage per box as well as individual tile size. Cross-check both figures – coverage per box is useful for estimating how many boxes to order.
Step 4: Apply the Correct Waste Allowance
Add 10–15% to your tile count to cover cuts, breakages, and future repairs – the exact percentage depends on tile size and layout pattern.
Waste is not optional padding. Cuts along edges and around fixtures consume whole tiles. Any breakages during installation are unrecoverable without spare stock.
Waste Percentage by Tile Size and Layout:
- Small format tiles (under 300 mm), straight lay: add 10%
- Standard format tiles (300–600 mm), straight lay: add 10–12%
- Large format tiles (above 600 mm), straight lay: add 12–15%
- Any size, diagonal or herringbone lay: add 15–20%
- Mosaic sheets: add 10% – cuts at edges are small but frequent
- Irregular or L-shaped rooms: always use the higher end of the range
The waste multiplier in the formula works as follows: a 10% allowance = multiply by 1.10; a 15% allowance = multiply by 1.15.
Step 5: Work Out the Total Number of Tiles
Divide total surface area by single tile area, multiply by the waste factor, and round up to the nearest whole tile.
Always round up. Half a tile does not cover half a surface.
Full Worked Example – Standard Family Bathroom
Room dimensions: 2.4 m × 1.8 m Tile chosen: 300 mm × 600 mm wall tile and 600 mm × 600 mm floor tile Tiling height: full ceiling at 2.4 m
Floor calculation:
- Floor area: 2.4 × 1.8 = 4.32 m²
- Single tile area: 0.6 × 0.6 = 0.36 m²
- Tiles needed: 4.32 ÷ 0.36 = 12 tiles
- Add 10% waste: 12 × 1.10 = 13.2 → order 14 tiles
Wall calculation (four walls, door deducted):
- Total gross wall area: (2 × 2.4 × 2.4) + (2 × 1.8 × 2.4) = 11.52 + 8.64 = 20.16 m²
- Deduct door: 20.16 − 1.54 = 18.62 m²
- Single tile area: 0.3 × 0.6 = 0.18 m²
- Tiles needed: 18.62 ÷ 0.18 = 103.4 tiles
- Add 10% waste: 103.4 × 1.10 = 113.7 → order 114 tiles
Step 6: Convert Tiles to Boxes
Divide your total tile count by the number of tiles per box, then round up to the nearest full box.
Never order partial boxes. Retailers sell by the box. A partial-box shortfall means ordering a full extra box anyway – often from a different production batch.
- Find tiles-per-box on the product specification or packaging label
- Divide total tiles needed by tiles per box
- Round up to the nearest whole number
- Example: 114 tiles ÷ 9 tiles per box = 12.67 → order 13 boxes
Checking Coverage Per Box
Most UK tile packaging states coverage in m² per box. If yours does:
- Total surface area ÷ m² per box = number of boxes before waste
- Multiply by your waste factor (1.10 to 1.20)
- Round up to the nearest full box
Both methods should produce the same answer. If they differ by more than one box, recheck your measurements.
Common Calculation Mistakes to Avoid
The most frequent tile ordering errors come from inconsistent units, forgotten deductions, and underestimated waste on diagonal layouts.
- Mixing mm and metres — convert everything to metres before calculating; never mix units mid-formula
- Forgetting partial walls — tiling to 1.2 m height is not the same as full-height; use actual tiling height
- Ignoring reveals — door and window reveals are small tiling surfaces; add them to wall totals
- Using the wrong waste % — diagonal and herringbone layouts waste 15–20%, not 10%; applying 10% leads to a shortfall
- Ordering from memory — always recheck the production batch number when reordering; colours vary between batches
What to Do With Leftover Tiles
Store surplus tiles flat, dry, and away from frost – they are essential for future repairs when the product line is discontinued.
Tile ranges change frequently. A cracked tile five years from now may be impossible to match if you have no spares. Keep at least five spare tiles per surface, regardless of project size.
- Label the box with room name, purchase date, and batch number
- Store horizontally – vertical storage risks chipping tile edges
- Keep the delivery note with batch and shade numbers attached
Accurate tile calculation follows six steps: measure floor area, measure wall areas individually, convert tile dimensions to metres, apply the correct waste percentage, round up to whole tiles, then convert to boxes. Use 10% waste for straight lays and 15–20% for diagonal or complex patterns. Order from one batch, store your spares, and keep the batch number – it will matter more than you expect when a tile needs replacing in three years.
Frequently Asked Questions
How much extra tile should I order for a straight lay pattern?
Add 10% for standard straight lay in tiles up to 600 mm. Increase to 12–15% for large-format tiles above 600 mm due to greater cutting loss at edges.
Do I need to deduct for the bath or shower tray?
Yes, if they sit against a tiled wall. Measure the bath panel or tray height and deduct that area from the relevant wall surfaces. Skipping this step leads to a modest overorder.
Should floor and wall tile orders be calculated separately?
Always. Floor tiles and wall tiles are often different sizes, finishes, and products. Combining them into one calculation produces the wrong totals for both surfaces.
What if I am tiling a shower enclosure separately?
Treat the shower enclosure as its own zone. Measure each internal wall, calculate tiles, and add 15% waste – shower enclosures involve more cuts around trays, niches, and fixtures than open walls.