How many square metres of flooring should I buy — and how much wastage should I allow for?
Buy the floor area plus wastage: 5-10% for ordinary straight laying, 10-15% for diagonal and 15-20% for herringbone — and always round up to whole packs.
Short answer: You need to buy the floor area plus a wastage allowance, then round up to whole packs, because flooring is sold by the pack — never in loose square metres. Allow 5-10% wastage for ordinary straight laying, 10-15% for diagonal laying and 15-20% for herringbone and chevron. A room of 17.4 m² laid straight thus becomes 17.4 × 1.07 = 18.6 m², and with packs of 2.22 m² you need to buy 9 packs = 19.98 m².
The calculation in three steps
The whole calculation of how much flooring to buy is three steps, in order. Take them in that order — swap steps 2 and 3 around, and you buy too little.
- Find the floor area — the internal area of the surfaces that are actually getting new flooring.
- Add wastage — a percentage that depends on the laying pattern and the room's shape.
- Round up to whole packs — and buy at least one extra pack as a reserve, if you can make use of it.
Step 1: Floor area is not the same as a home's registered area
The floor area is what you measure internally from wall to wall in the room getting new flooring. As a rule, that is smaller than the figure in the housing register: the register typically states the home's area measured to the outside of the external walls, and the internal partition walls are included — while the flooring only sits on the internal space.
In an ordinary detached house, that difference is often 10-15%. A house registered at 120 m² routinely has only 102-108 m² of internal floor, and a small home loses relatively more still to the walls, because the perimeter takes up more per square metre. So if you calculate from the register's figure, you buy a good deal too much.
Measure each wall internally at floor height, not at hip height. Skirting boards, out-of-plumb walls and old rendered masonry make a difference down there, where the flooring is actually going. If the room is rectangular, the area is length × width. If the room has a step, a niche or a bay, split it into rectangles and add them up.
Example: A living room measures 4.12 m × 3.05 m = 12.57 m². The hallway next to it measures 1.20 m × 4.00 m = 4.80 m². Total floor area = 17.37 m².
What you don't subtract: doorways (the flooring typically has to run through them), radiator pipes and small items. What you can subtract are fixed installations the flooring doesn't run under: a built-in shower enclosure, a fixed hearth, a fitted kitchen unit standing on the floor — but if you do subtract them, remember the flooring still has to be cut around them, and that cutting wastage has to be added back in. In practice it's often wisest to just leave small fixed items in the area.
If you have a measured floor plan of the home, the floor area per room is already sitting there. HouseSense calculates the area per room from the scanned or drawn plan, so you don't have to multiply and add by hand — but whichever method you use, the same rule applies: the figure has to be the internal one, not the register's.
Step 2: How much wastage should you allow for?
Wastage is the flooring you buy and don't end up laying: offcuts at the ends of rows, boards cut around door frames and pipes, boards discarded because of a knot or a defect, and the pieces left too short to use. The wastage percentage depends almost entirely on the laying pattern.
- Straight laying, single rectangular room: 5-7%. The boards run parallel to one wall, and the offcut from the end of one row can start the next.
- Straight laying, room with many corners, niches or a staircase: 8-10%. Every extra edge costs a cut, and every cut costs a piece.
- Diagonal laying (45° to the walls): 10-15%. Every board has to be cut at an angle at both ends, and the triangles along the walls can rarely be reused.
- Herringbone and chevron: 15-20%. The pattern has to work out against all four walls, and the edge rows turn into triangles and short pieces that can't be reused. Chevron boards are even angle-cut at the factory into left- and right-hand versions, so you can't just flip a piece over.
- Very long, narrow rooms and hallways: add 2-3 percentage points regardless of pattern. A 1.2 m wide hallway gives many rows with only one cut to spread the wastage across.
- Large, long boards (2 m and up): add 2-3 percentage points. The longer the board, the bigger the piece left over at the end of the row.
Be aware that the supplier's own instructions always take precedence over these rules of thumb. Some manufacturers specify a particular allowance for their exact product and laying pattern, and some supply herringbone in sets where the wastage is already factored in. If the fitting guide says something, that's what applies — including to your tradesperson.
Step 3: Round up to whole packs
Flooring is sold by the pack, not by the square metre. A pack of laminate typically covers 1.7-2.7 m², a pack of engineered wood typically 1.5-3.5 m², and a pack of vinyl planks typically 1.5-2.5 m² — the exact figure is always printed on the pack's label. You can't buy 8.37 packs.
The calculation, finished: The floor area is 17.37 m². Straight laying in two rooms with a couple of corners gives 7% wastage: 17.37 × 1.07 = 18.59 m². The pack covers 2.22 m²: 18.59 ÷ 2.22 = 8.37 packs → round up to 9 packs = 19.98 m². You now have 2.61 m² left over.
The same flooring laid herringbone: 17.37 × 1.18 = 20.50 m² → 20.50 ÷ 2.22 = 9.23 → 10 packs = 22.20 m². The pattern alone costs one extra pack in this room.
Why you should buy one pack extra on top
The flooring you have left over isn't waste — it's spare parts. Flooring is produced in batches, and colour and grain vary between batches. In two years' time, when a washing machine has leaked or a piece of furniture has scored three boards, you can rarely buy exactly the same flooring from the same batch again. An unopened pack in the loft is the difference between replacing three boards and replacing the whole floor.
Set against each other, the choice isn't hard: the extra pack costs a fraction of what it costs to relay a whole room. Also check the shop's return policy before you buy — many take unopened packs back within a window, in which case the extra pack is effectively free insurance.
How to avoid the three classic mistakes
Mistake 1: calculating from the registered housing area. The register's figure is as a rule measured externally and covers the whole home. The flooring only needs to run internally in the rooms you're renovating. Measure it yourself, or use the areas from a measured floor plan.
Mistake 2: forgetting that wastage is added before rounding to packs. Round up to packs first and add wastage afterwards, and you get a wrong — and almost always too low — figure.
Mistake 3: ordering in two batches. The second order comes from a different batch, and the colour difference shows in raking light. Order the whole floor in one go, including the spare pack.
If you don't know the room's measurements
If you need the floor area and don't have the measurements, there are two routes. Either you measure each wall internally with a tape measure or laser distance meter and multiply — and measure the diagonal too, so you can see whether the room is even square. Or you make a measured floor plan, which gives you the area per room directly. HouseSense makes that plan either by scanning the room with the iPhone's LiDAR, or by you drawing the room with your finger and typing in the measured centimetres. Both routes end up in the same place: an internal floor area per room that you can multiply by the wastage percentage.