How to use the Tile Calculator
- Enter the room dimensions, measuring each rectangular area separately.
- Enter the tile size and the number of tiles per box.
- Choose the layout — straight, diagonal or herringbone — to set the waste allowance.
- Round up to whole boxes and buy one extra for future repairs.
How the calculation works
Divide the total area by the area of one tile to get a base count, then apply a waste factor. Straight-laid tiles in a simple rectangular room waste around 10%; diagonal layouts waste 15% because every perimeter tile is cut on an angle, and herringbone or complex patterns can reach 20% or more. Rooms with alcoves, thresholds and pipe boxings raise it further, since each cut produces an offcut too small to use elsewhere.
Buy from a single production batch. Tile shade varies measurably between batches, so a top-up order weeks later often will not match the original, which is why an extra box kept aside for future repairs is standard practice. Grout joint width also affects the count slightly on small formats — a 3 mm joint across a mosaic makes a real difference, though it is negligible on large-format tiles.
Tiles = (area / tile area) × (1 + waste) ; Boxes = ceil(tiles / tiles per box)Source: Standard tiling waste allowances per Tile Council of North America and British Standard BS 5385 installation guidance.
Worked example
A bathroom floor 2.7 m × 2.1 m laid diagonally in 300 × 300 mm tiles, 11 tiles per box.
- Area = 2.7 × 2.1 = 5.67 m².
- Tile area = 0.09 m², so base count = 5.67 / 0.09 = 63 tiles.
- Diagonal layout waste at 15%: 63 × 1.15 = 72.5, round to 73.
- Boxes = 73 / 11 = 6.6, round up to 7.
Seven boxes, giving 77 tiles — four spare for future repairs, from the same batch.
Frequently asked questions
How much waste should I allow?+
10% for straight layouts in simple rooms, 15% for diagonal, and up to 20% for herringbone or rooms with many corners and alcoves.
Why buy from the same batch?+
Ceramic and porcelain shade varies between production runs. A replacement box bought later is likely to be visibly different, which matters most on large uninterrupted floors.
Should I subtract doorways and fittings?+
Subtract only substantial areas such as a bath footprint or a fitted island. Small exclusions are effectively absorbed by the waste allowance, and subtracting them risks ordering short.
Do grout joints change the tile count?+
Slightly, and mostly on small formats. A 3 mm joint across mosaic tiles reduces the count measurably; on 600 mm tiles the effect is well within the waste allowance.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.