Materials
Flooring Calculator
Convert room dimensions into boxes of flooring with the right waste factor, plus underlay and cost.
Your answer
Keep one full box back as spares — matching a discontinued range later is usually impossible.
How flooring quantities are worked out
Flooring is sold by the box, and each box states the area it covers. The calculation is therefore room area, plus a waste allowance, divided by box coverage, always rounded up. The waste allowance is where most orders go wrong: it is not a safety margin you can trim, it is the offcut you physically cannot use.
Every row ends with a cut. That offcut starts the next row only if it is longer than the minimum plank length the manufacturer allows — usually around 300 mm. Anything shorter goes in the bin. Across a whole room this recurring loss lands consistently around ten per cent for a straight lay.
Why pattern changes the number so much
| Lay pattern | Waste factor | Why |
|---|---|---|
| Straight, simple rectangle | 10% | Only end cuts and the final row |
| Straight, room with alcoves | 12-15% | Each obstruction creates unusable offcuts |
| Diagonal (45°) | 15% | Every plank meets a wall at an angle |
| Herringbone / chevron | 20% | Every piece is cut, and the perimeter is complex |
A worked example
A 12 by 14 foot room is 168 square feet. A straight lay adds 10%, giving 185 square feet to order. At 20 square feet per box that is 9.25 boxes, so you buy 10. The tenth box is your spare — which is exactly the buffer you want anyway.
Do not forget the layers under the boards
- Damp-proof membrane over any concrete subfloor, even one that feels dry.
- Underlay for floating floors — acoustic performance and comfort both depend on it.
- Levelling compound if the subfloor deviates more than about 3 mm over 2 m.
- Beading or skirting to hide the expansion gap around the perimeter.
- Threshold strips at every doorway and material change.
Common mistakes
- Ordering exactly the room area and running short on the final row.
- Skipping acclimation — boards need days in the room before they are laid.
- Closing the expansion gap with sealant, which causes the floor to peak in the middle.
- Mixing batches bought months apart, so shade and gloss differ across the room.
- Laying over an unlevel subfloor and blaming the boards for the movement.
How much extra flooring should I order?
Ten per cent for a straight lay in a simple rectangle, fifteen per cent for rooms with alcoves or a diagonal lay, and twenty per cent for herringbone or chevron.
Should I buy a spare box?
Yes. Ranges are discontinued constantly, and a future repair needs boards from the same batch. One spare box stored flat is cheap insurance.
Do I need underlay?
Floating floors need it for acoustics, comfort, and moisture control. Glued or nailed floors usually do not, but a damp-proof membrane over concrete is still essential.
How big should the expansion gap be?
Roughly 10-12 mm at every wall and fixed object for wood and laminate. It is hidden by skirting or beading and must never be filled with adhesive.
Last reviewed February 2026