How much waste should I really allow?

8% for a straightforward rectangular room laid straight, 10% if the room has bays or many doorways, 15% or more for diagonal and herringbone. The offcut from the end of one row often starts the next, which is why straight lays waste so little.

Do I need expansion gaps?

Yes for any floating floor — typically 10–12 mm around the entire perimeter, hidden by skirting or beading. This does not change the quantity you buy, but skipping it is what makes a floor buckle in summer.

Flooring Calculator

Calculate how much flooring material you need and estimate cost. Includes waste margin.

Room length (m)

Room width (m)

Price per box

Box coverage (m²)

Printed on the pack — commonly 1.8 to 3.3 m².

Waste margin (%)

Flooring: area, waste and why the offcuts matter

Floor area is the easy part. What decides whether you have enough is the waste allowance, and that depends on how the planks are laid rather than on the size of the room.

How it works

Multiplies length by width for each rectangular area and totals them.
Adds a waste percentage for cuts at the walls, and more for diagonal or herringbone layouts.
Converts the total into whole packs, since flooring is sold by the pack and part packs are not.

area   = Σ (length × width)
packs  = ceil(area × (1 + waste) ÷ pack coverage)

waste allowance by layout
  straight, rectangular room     5–8%
  straight, awkward shape        10%
  diagonal                       15%
  herringbone or chevron         15–20%

Worked example

A 5.2 × 3.8 m living room, straight-laid, with packs covering 2.2 m² each.

area = 5.2 × 3.8 = 19.76 m²
add 8% waste → 19.76 × 1.08 = 21.34 m²
packs = 21.34 ÷ 2.2 = 9.7
round up → 10 packs (22 m²)

Ten packs, leaving about 0.66 m² spare. That spare is the point — keep it for a future repair, because matching a discontinued batch later is usually impossible.

Reading the result

Buy one extra pack beyond the calculation and keep it sealed. Flooring batches vary in shade and are discontinued regularly; a damaged plank in year three is unfixable without it.
Waste is driven by layout, not room size. A herringbone floor needs roughly double the offcut allowance of a straight lay, because every plank meets an angle.
Measure the widest points including doorways and alcoves, and treat each rectangle separately rather than averaging an irregular room.
Underlay is a separate calculation and usually comes in rolls with different coverage. It does not need the same waste allowance, since it can be butted and taped.

Common questions

How much waste should I really allow?: 8% for a straightforward rectangular room laid straight, 10% if the room has bays or many doorways, 15% or more for diagonal and herringbone. The offcut from the end of one row often starts the next, which is why straight lays waste so little.
Do I need expansion gaps?: Yes for any floating floor — typically 10–12 mm around the entire perimeter, hidden by skirting or beading. This does not change the quantity you buy, but skipping it is what makes a floor buckle in summer.