Tile Quantities and Wastage: A Worked Ordering Calculation

Ordering tiles on net floor area is the most common way to run out mid-job. This illustrative calculation shows how to get from measured area to boxes ordered.

Tiles are sold in boxes, laid with cuts and breakages, and produced in batches that do not match each other. Those three facts mean the quantity you order is never the area you measured. This worked example takes one illustrative apartment from measured areas through wastage and box sizes to a final order, and compares the result with ordering on net area alone. Every figure is an invented assumption used to show the method rather than a price or a market rate.

The situation

An owner is retiling a 90 square metre apartment before letting it: an open living and dining area, two bedrooms, a corridor and two bathrooms. The living area will be laid diagonally because the room is wider than it is deep and the diagonal pattern suits the sightline from the entrance; everywhere else is a straight lay. The owner wants to know how many boxes to order, how much to keep as attic stock, and how far an order based on net area alone would fall short.

Assumptions (illustrative)

• Net floor areas: living and dining 46 square metres, bedrooms 14 and 12 square metres, corridor 8 square metres.
• Floor tile 600 by 600 millimetres, four tiles per box, giving 1.44 square metres per box.
• Wastage assumed at 15% for the diagonal living area and 8% for the straight-laid rooms.
• Two bathrooms, each with a wall perimeter of 9.6 metres and a wall height of 2.4 metres, less one door opening of 1.8 square metres each.
• Wall tile 300 by 600 millimetres, eight tiles per box, giving 1.44 square metres per box, with wastage assumed at 12% because of the cutting around fittings.
• Illustrative supply rates: 95 SAR per square metre for the floor tile and 80 SAR per square metre for the wall tile.

Step 1: Total the net floor areas

46 plus 14 plus 12 plus 8 gives 80 square metres of net floor area across the four dry areas.

This is the figure most people order against, and it is the figure that guarantees a shortfall. It represents the area the tiles must cover, not the quantity that must be bought, because every cut tile leaves an offcut that usually cannot be used elsewhere.

Step 2: Apply wastage according to the laying pattern

The living area at 46 square metres with 15% wastage becomes 46 multiplied by 1.15, which is 52.9 square metres. The remaining 34 square metres with 8% wastage becomes 34 multiplied by 1.08, which is 36.72 square metres. The total required is 52.9 plus 36.72, which is 89.62 square metres.

Wastage is not a single percentage applied to a whole job. A diagonal lay generates cuts along every wall and the offcuts are triangular and unusable, which is why it carries roughly double the allowance of a straight lay. Deciding the pattern before ordering is therefore a procurement decision as much as an aesthetic one.

Step 3: Convert the requirement into whole boxes

89.62 divided by 1.44 square metres per box gives 62.24 boxes, which rounds up to 63 boxes. Sixty-three boxes supply 63 multiplied by 1.44, which is 90.72 square metres.

Rounding is always upward and always to a whole box, because suppliers do not split them. The rounding alone adds a little over one square metre here, which is useful rather than wasted, since it goes towards the next step.

Step 4: Add attic stock for future repairs

Adding two boxes for attic stock takes the order to 65 boxes, supplying 65 multiplied by 1.44, which is 93.6 square metres.

Attic stock is the cheapest insurance in an interior. Tiles are produced in batches with shade variation, so a replacement bought in two years is unlikely to match. Two boxes held in a store will repair a damaged area in any room; two boxes not held means replacing a whole floor to keep it consistent.

Step 5: Calculate the bathroom wall tiles

Each bathroom gives 9.6 metres multiplied by 2.4 metres, which is 23.04 square metres, less 1.8 square metres for the door opening, which is 21.24 square metres. Two bathrooms give 42.48 square metres. With 12% wastage this becomes 47.58 square metres, which divided by 1.44 gives 33.04 boxes, rounding up to 34 boxes supplying 48.96 square metres.

Wall tiling carries a higher wastage allowance than floors because of the cutting around pipework, niches, fittings and switch plates, and because the setting-out usually requires a cut course at one end. Deducting the door opening but not the window or mirror positions keeps the calculation conservative, which is the right direction for an order.

Step 6: Compare the full order with an order based on net area

The correct order costs 93.6 multiplied by 95 SAR, which is 8,892 SAR, plus 48.96 multiplied by 80 SAR, which is 3,916.80 SAR, giving 12,808.80 SAR. Ordering on net area would have given 80 multiplied by 95, which is 7,600 SAR, plus 42.48 multiplied by 80, which is 3,398.40 SAR, totalling 10,998.40 SAR. The shortfall is 1,810.40 SAR, which is about 16.5%.

The net area order is not a 16.5% saving but a 16.5% shortfall, discovered when the tiler runs out with the corridor unfinished. A second order then arrives from a different batch, and the repair is visible for the life of the floor. The arithmetic matters because the consequence is not a cost overrun but a permanent defect.

What changes the answer

• If the tile format is larger, breakage during cutting rises and the wastage allowance should increase above the figures used here.
• If a patterned or herringbone lay is chosen rather than a diagonal one, the wastage can exceed the 15% assumed for the living area.
• If the rooms are out of square, cuts are tapered rather than straight and offcuts become unusable, pushing actual wastage higher.
• If the supplier can guarantee a single batch for the whole order, attic stock is less critical, but that guarantee should be obtained in writing before relying on it.
• If the tiles are imported, conformity documentation becomes a programme risk, since products subject to Saudi standards need valid certificates to clear through the SABER platform.

What the numbers tell you

• Order against required area after wastage and rounding, never against the net area you measured.
• Wastage depends on the laying pattern, the format and the squareness of the room, so it has to be set per area rather than as one project figure.
• Always round up to whole boxes and then add attic stock deliberately, treating it as part of the specification rather than a leftover.
• A shortfall is more damaging than an overspend, because a second batch rarely matches and the mismatch is permanent.
• Prices, tax treatment and certification requirements change over time, so confirm current rates and conformity requirements with your supplier, ZATCA and the relevant authority before ordering, and take any contractual question to a licensed adviser.

Limits of this example

Every figure above is an illustrative assumption used to show the method, not a quote, valuation or market rate. Costs, rates, fees and regulations change and must be confirmed with the relevant authority, lender or supplier before you commit.

Domira designs and delivers interiors as part of the building, not after it: the finishing schedule, the joinery and the services coordination that decide whether a space looks built or assembled. Share the space and Domira will tell you what it would specify and what it would leave out.