Room area is the starting number, not the order quantity. A narrow strip along the wall still consumes part of a tile, and an offcut is useful only if its size, edge and pattern suit another position.
Start with the actual tiled surfaces
Measure each floor or wall plane separately. Include returns, niches and exposed edges where they are being tiled. Record deductions explicitly rather than subtracting every small opening and hoping the remaining offcuts work out.
Choose the tile size, joint width and laying pattern before finalizing the count. A diagonal layout, directional design or vein-matched feature changes which cuts can be reused. Ask the installer to review the layout at doorways and prominent edges before placing the order.
Measured coverage
List each tiled plane and any deliberate deductions.
Layout pieces
Count tiles needed for the chosen pattern and cut edges.
Working allowance
Agree handling and installation allowance with the installer.
Reserved spares
Add repair stock, then round to purchasable cartons.
Separate three different allowances
Cutting loss covers pieces consumed by the layout. Breakage allowance covers handling and installation losses. Repair stock is material intentionally kept after completion. If all three are hidden inside one percentage, it is easy to discover that the 'spares' were used to finish the room.
Daltile: tile and natural stone FAQs recommends keeping additional matching tile for future repairs and notes that production can vary. That supports a deliberate spare-stock decision; it does not make one percentage a complete takeoff for every pattern.
Work in pieces and cartons
For a small room with large tiles, draw the rows and count whole pieces needed for edge cuts. Compare that with the supplier's carton coverage. Rounding to full cartons can matter more than a decimal place in the room area. For example, suppose the checked layout consumes 48 tiles, including the whole tiles needed to make the edge cuts. You agree on 3 additional tiles for handling losses and keep 4 untouched tiles for future repairs. That is 48 + 3 + 4 = 55 tiles. At 6 tiles per carton, round 55 / 6 up to 10 cartons: 60 tiles delivered. If the planned losses occur, the remaining 9 tiles include your 4 reserved repair pieces and 5 from carton rounding.
The example's 3-tile handling allowance and 4-tile repair reserve are choices for that order, not percentages to copy onto every room. Count an offcut twice only when the layout really uses both pieces, allowing for the saw cut and required finished edges. Check trims, skirtings and special pieces separately. Do not assume a field-tile allowance includes the corner pieces for a niche or the bullnose around an opening. Confirm what can be returned and by when; special orders and opened cartons may have different terms.
Protect the matching supply
At delivery, compare product, shade and batch labels before installation. Keep labelled repair stock aside and tell the installer it is reserved. For patterned or variable material, review several pieces together rather than one tile from the top of a box.
Store the remainder using the surplus-material plan, with the product identity still attached. A matching tile five years later is far more useful than a photograph of an empty carton. If the pattern is still undecided, make a sample layout before ordering rather than buying extra to cover indecision.