Flooring is quoted per square metre and sold by the pack, and the gap between those two facts is where budgets go. This draws the floor as you measure it — rectangle, L shape or tapered — adds the cutting waste your layout will actually produce, and converts the result into packs and into metres of skirting, which is a separate purchase that people forget until the floor is down and the gap is showing.
The floor
Most rooms are one of these three shapes; the tapered one covers bay windows and walls that follow a staircase or a roof line.
Fine tuning
7 to 8% straight lay, 12 to 15% diagonal, 15% or more for herringbone.
Result
The room is rarely the shape the estate agent's plan says
Floor plans are drawn to sell, not to measure. They show a neat rectangle with a door in it, and the room has a chimney breast that takes 600 mm out of one wall, an alcove either side of it, a bay that widens one end by a metre, and a corner the stairs cut through. None of that changes the plan, because the plan is not trying to be a survey.
The consequences are financial and immediate. Flooring is sold in whole packs with a coverage printed on the side, and the gap between the measured area and the number of packs is not negotiable at the counter. Order eleven packs when you need twelve and the job stops until the second delivery, which will be from a different batch — and batch variation is visible on a floor in a way it never is on a wall.
Three shapes cover almost every floor
What matters is not how closely the shape matches, but which decomposition loses the least ground. A room that is technically six-sided is usually a rectangle plus a triangle, and working it that way is both faster and more accurate than trying to fit it to something else.
The default, and usually wrong
- Two measurements, one multiplication.
- Check both diagonals: if they differ by more than 20 mm, it is not a rectangle.
- Older houses are almost never square.
Chimney breast, stair box, fitted cupboard
- Measure the full outline, then the projection that is not floor.
- Area is outline minus projection.
- The skirting run is the outline perimeter, unchanged by the projection.
Bay window, sloping wall, loft
- Two parallel ends and the perpendicular distance between them.
- Average the ends and multiply by the distance.
- Used more often than people expect, because bays are common.
A projection into a room removes floor area but adds exactly as much wall as it removes, so the perimeter of an L-shaped room is identical to the rectangle it was cut from: 2 × (width + depth).
Order skirting off the outline. Order flooring off the net area. They come from the same two measurements and they differ by the projection, which is why buying them from a single figure leaves you short of one or with a roll of the other left over.
Measuring a room properly
Flooring needs the dimensions clear of the skirting, because boards and sheets go under it. Measuring over the top of skirting adds 18 mm per wall, which on a 4 m × 5 m room is about 0.3 m² — small, but it is the difference between eleven packs and twelve at the margin.
- Measure wall to wall, floor levelTape against the skirting or under it. Not over furniture, not around it.
- Take width at both endsRooms taper. If the two widths differ by more than 20 mm, use the tapered shape and the average, rather than pretending they match.
- Measure into reveals and baysA bay is floor. A door reveal usually is not, but the threshold strip is a separate purchase.
- Note everything that is not floorChimney breasts, stair boxes, fitted units on plinths. Subtract them, or use the L shape.
- Write it down in metres with two decimals4.20 m, not 4 m 20. Mixing units in a multiplication is how 22.68 becomes 24.
Do
- Measure at floor level, clear of the skirting, wall to wall.
- Check both diagonals before assuming a rectangle.
- Measure the width at both ends of the room.
- Subtract fixed units sitting on plinths; they are not floor.
Avoid
- Measuring over the top of the skirting and calling it the floor.
- Using the widest wall as the width when the room tapers.
- Forgetting door thresholds, which are a per-door purchase.
- Ordering on the measured area without any waste allowance at all.
Waste is not a fudge factor
The cutting allowance is not there to cover bad measurement. It is the physical consequence of laying rectangles into a space that does not divide by the board length. Every row ends with an offcut, and whether that offcut starts the next row depends on the layout.
| Pattern | Waste | Why |
|---|---|---|
| Straight, plank, rectangular room | 7 to 8% | One offcut per row, most of them reusable |
| Straight, plank, L-shaped room | 10 to 12% | Offcuts from the notch rarely fit elsewhere |
| Diagonal at 45 degrees | 12 to 15% | Every edge is a cut and both ends of every row are waste |
| Herringbone | 15 to 18% | The pattern eats board length at every boundary |
| Sheet vinyl, single seam | 5% | Large sheets, few cuts, but the seam has to be placed |
| Tile, 300 mm, straight | 10% | Grouted joints mean offcuts are shorter and less reusable |
There is a second kind of waste that no percentage covers: the damaged pack. Boards arrive with transit damage, and laminate in particular chips at the tongue if the pack has been dropped. On a job of more than about ten packs, one in ten will have a board you cannot use. That is what the surplus from rounding up to whole packs is for — which is why the answer here is always rounded up, never down.
What the area turns into
Floor area is the input to four separate purchases: the flooring itself, the underlay, the skirting or beading, and the threshold strips. The first two are per square metre, the third is per metre of perimeter, and the fourth is per door, which is why a single figure cannot cover all of them.
The skirting length calculator takes the perimeter and works out how many lengths to buy, and the flooring calculator goes into the board-by-board detail if you want the layout planned rather than just quantified. For a room where the question is what size of rug fits rather than what it costs to cover, the rug size calculator and the furniture fit calculator both start from the same two dimensions.
Walls are a different calculation entirely, because they are measured in elevation rather than plan and have openings taken out of them: the wall area calculator handles that, and the paint calculator turns it into tins. Where several rooms share one order, the multi-room material figure keeps the pack count honest across all of them.
A worked example
A living room with a chimney breast, which is the standard awkward case in any house built before about 1960.
- The outlineWall to wall at floor level: 5.5 m by 4.8 m, so the outline is 26.4 m².
- The chimney breastIt projects 1.8 m into the room and is 2.2 m wide: 3.96 m² of floor that does not exist.
- Net floor26.4 − 3.96 = 22.44 m². Using the outline would have bought flooring for a fireplace.
- WasteStraight lay in an L-shaped room, so 12%: 25.13 m² to order.
- PacksAt 2.2 m² per pack that is 11.4, so 12 packs, and the twelfth is mostly the damaged-board allowance.
- Skirting2 × (5.5 + 4.8) = 20.6 m, because the breast adds as much wall as it removes floor.
What the covering does to the waste figure
The waste percentage is a property of the material as much as of the pattern. Sheet materials waste at the edges only; plank materials waste at the end of every row; tiles waste at every row and every cut, and the offcut from a tile is nearly always too small to use because grouted joints consume it.
| Covering | Waste | What drives it |
|---|---|---|
| Sheet vinyl, one seam | 5% | One cut per wall, the seam placed away from the door |
| Laminate plank, straight | 8% | One offcut per row, most reusable at the other end |
| Engineered board, straight | 10% | Longer boards, fewer reusable offcuts, more grading out |
| Solid wood, straight | 12% | Grading for colour and defects before laying |
| Ceramic tile, straight | 10% | Joint width plus breakages plus cuts at every boundary |
| Carpet, 4 m width | 8 to 15% | Room width against the roll width; a 4.2 m room wastes a metre |
Carpet deserves a note because it is the one covering where the room's width matters more than its area. Carpet comes in fixed widths, usually 4 m, and a room 4.2 m wide needs a join or wastes a metre of roll along its whole length. That is why a 4.2 × 5.4 m room can need more carpet than a 4.0 × 6.0 m one despite being smaller, and it is the one case where the area alone will mislead you.
Heating, build-up and the height you have not got
Floor area is measured in plan, but what goes into it has a thickness, and the thickness has consequences for doors, thresholds and appliances. A typical build-up — underlay, board, and skirting to cover the expansion gap — adds 15 to 20 mm. Underfloor heating under tile adds 60 mm or more including the screed.
Going from sheet vinyl to engineered board means trimming doors, refitting thresholds and, in a kitchen, checking that the dishwasher still comes out. None of that appears in a square-metre figure.
Measure the existing floor-to-door gap before choosing anything. If it is under 20 mm, the build-up decides what you can lay, not the area.
Underfloor heating also changes which way the waste calculation goes. It makes large format tile more attractive, because fewer joints means better heat transfer, and it makes thick underlay under laminate a poor choice, because it insulates the very thing you are paying to run. Check the tog rating on any underlay going over a heated floor: above about 1.5 tog the system is heating the underlay.
Where the numbers stop being true
This works on plan area at floor level. It does not account for a floor that is not level, which matters more than it sounds: a floor out by more than about 3 mm over a metre needs levelling compound before anything goes down, and levelling is priced by the bag per square metre at a depth you cannot know until you have surveyed it.
It also assumes the packs you buy are the size printed on them, which is usually true and occasionally not. Own-brand laminate in particular varies by 5% between ranges. Check the coverage on the actual pack, not on the website, before trusting the pack count.
Before you order
- Measure at floor level, wall to wall, clear of the skirting.
- Take the width at both ends and use the tapered shape if they differ.
- Subtract chimney breasts, stair boxes and units on plinths.
- Set the waste from the laying pattern, not from habit.
- Round packs up, never down, and keep one pack unopened for repairs.
- Order skirting off the perimeter as a separate line.
How the arithmetic works
Rectangle: width × length, perimeter 2 × (width + length). L shape: (overall width × overall depth) − (projection width × projection depth), perimeter 2 × (width + depth) because the projection adds back what it removes. Tapered: (narrow end + wide end) ÷ 2 × the perpendicular distance between them, with the sloping sides worked out from the offset and the length.
Order quantity is the net area × (1 + waste ÷ 100). Packs are the order quantity divided by the pack coverage, rounded up, because a part pack is still a pack you have to buy. Square feet are square metres × 10.7639.
Questions people ask
Do I subtract the area under fitted wardrobes?
If they sit on a plinth and will stay, yes — flooring does not go under them. If they are freestanding and might move, floor the whole room; the cost of the extra couple of square metres is far less than the cost of a room with a bare strip behind where the wardrobe used to be.
Why is the skirting run the same as the outline?
Because a chimney breast removes floor but replaces it with the same length of wall. The perimeter of an L-shaped room is identical to the rectangle it was cut from, so skirting comes off the outline and flooring comes off the net area.
How much waste should I allow for a bay window?
Treat the bay as part of a tapered room, then add 3% on top of the pattern waste, because bays are usually laid with cuts radiating from the centre and every one of them is a one-off.
Should I order extra for repairs?
One unopened pack, kept flat and dry. Flooring ranges are discontinued on a cycle of roughly two years, and a repair three years later without spare board means replacing the whole floor or living with the patch.
What if the room has a staircase in it?
Measure the floor around it, and treat the stairs as a separate job priced per tread. The two are different trades, different materials and different units, and combining them into one area produces a number that is wrong for both.
Is area enough, or do I need a layout plan?
For ordering, area plus the right waste figure is enough. For laying, you want the row widths worked out, because a room that finishes on a 40 mm sliver against the far wall looks wrong no matter how good the floor is — that is a layout question, not a quantity one.