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How do you work out materials in packs — and should you add waste?

Flooring, tiles and skirting are sold in fixed pack sizes, not by the loose metre. Here is how to round correctly from square metres to packs, and how much waste to add on top, depending on the pattern.

Why materials are sold in packs, not loose by weight

Floorboards, tiles, skirting and many kinds of insulation are packed into fixed units because that is how they are produced, transported and stocked. A pallet of flooring holds a fixed number of packs, a pack holds a fixed number of boards, and a board has a fixed size. That means you can rarely buy "exactly 14.7 m²" — you buy the number of whole packs that cover that area, plus whatever you throw away in cutting.

How to work out packs from square metres

The method is the same whether it is flooring, tiles or skirting:

1. Find the room's net area — the floor surface that actually needs covering, not the gross area including wall thickness.
2. Add waste on top, according to the pattern and the shape of the room (see the next section).
3. Divide the total by how many square metres one pack covers. That figure is printed on the pack or in the product sheet.
4. Always round up to the nearest whole pack. Never down, and never to the nearest half.

Round down and you end up with a hole in the floor when the last board runs out, plus an urgent reorder — often from a different production batch, which can carry a visibly different shade.

How much waste to allow — and why

Waste is the part of the material that gets cut off and discarded at corners, along walls and around doorways. How much depends on the pattern and the shape of the room:

• Straight lay, parallel to the wall, rectangular room: 5-8 % waste is normal.
• Diagonal lay: 12-15 %, because every board along the edge is cut at an angle, and the offcut can rarely be reused.
• Herringbone and other patterns with short pieces: 15-20 %, because each individual piece has a fixed length, and a room rarely divides into whole units.
• Irregular rooms, alcoves and bay windows: add a further 3-5 % regardless of pattern, because every awkward corner needs a piece cut to fit that cannot be used again elsewhere.

Worked example: flooring for a 14.7 m² room

A 14.7 m² room is to have flooring laid in herringbone. The waste allowance is set at 18 %:

14.7 m² × 1.18 = 17.35 m² total requirement.

If the flooring is sold in packs of 1.9 m², the sum is 17.35 ÷ 1.9 = 9.13 — rounded up to 10 packs. Had you calculated only the net area with no waste (14.7 ÷ 1.9 = 7.7, rounded to 8 packs), you would be two whole packs short with the contractor halfway through the job.

When to round up per room, and when for the whole home

For flooring with a direction and visible colour variation, you should always round up per room rather than adding several rooms' areas together first. Two rooms of 7.4 m² each do not necessarily need the same number of packs as one room of 14.8 m², because the cutting along walls and doorways happens twice, not once. Materials with no direction or visible joint — like loose insulation — can, by contrast, often be calculated together for the whole home, because there is no visual boundary the waste has to fit within.

Tiles and grout follow the same principle, different figures

Tiles are calculated the same way, but typically with lower waste for a straight lay (5-10 %) and markedly higher for diagonal (15-20 %) or irregular formats. Also remember to count tile adhesive and grout as their own line items, not part of the tile pack — they are sold by coverage per bag, which depends on tile size and joint width, and should be calculated separately.

Paint — litres, not packs, but the same logic

Paint is not sold in packs, but the principle of rounding up is the same. The coverage figure on the tin (typically 8-10 m² per litre for an ordinary wall paint) is measured on a smooth, prepared surface — a rough or porous wall, or a dark base being painted light, will take more. Allow for two coats as standard, and always round up to the nearest whole tin, for the same reason as with flooring: a partly painted wall where the paint ran out is hard to match exactly, even with the same product code.

What happens if you get the sum wrong

The most common consequence is not that the work stops — it is that the reorder comes from a different production batch. Flooring, tiles and paint are produced in batches, and even the same product code can show a visible difference in shade between two batches. It shows up most clearly on large, single-colour surfaces in daylight — a floor that meets two colour batches halfway across a room is hard to correct afterwards without relaying it.

"Can I not just buy a bit extra to be safe?"

That is a common shortcut — buy 20 % extra of everything, and the problem is solved. It is not wrong, but it costs more than necessary on large areas and too little on small, irregular rooms. A generous standard like 20 % suits a small, irregular room with many corners well, but is pure overbuying in a large, rectangular living room, where 6-8 % is plenty. Use the specific figures for pattern and room shape rather than one fixed percentage for the whole home — the difference between 8 % and 20 % of a 40 m² floor is a substantial amount of surplus material that never gets used.

Keep the leftover pack — but write down the batch number

If you have followed the rule of rounding up, you often end up with broken packs, or a single whole pack left unused. Keep it for repairs later — but note the batch or lot number from the packaging first, and store it with the rest of the home's paperwork. If you need to repair a single board or tile some years from now, that is the piece of information that decides whether the replacement matches, or whether the whole surface has to be redone to avoid a visible shift in shade.

What HouseSense does

In HouseSense, a budget line can be priced either per square metre or as a pack price. Choose pack price and the app automatically rounds up per room based on the room's actual area; choose per-m² pricing and the area is used directly, with no rounding. The waste percentage is still yours to judge, based on pattern and room shape — that is a trade judgement the app cannot make for you.

Checklist before you order

1. Measure the room's actual area — net, not including wall thickness.
2. Choose a waste percentage by pattern: 5-8 % straight lay, 12-20 % diagonal or herringbone.
3. Always round up to the nearest whole pack — never down.
4. Order it all at once if you can, to avoid different production batches.
5. Calculate adhesive, grout and primer as their own line items with their own coverage.