Flooring and Tile Calculator
Boxes of flooring or tiles for a room, with a wastage allowance that reflects how you are laying it.
In short
Divide the room area by the coverage per box, then add a wastage allowance for offcuts: 10% for a straight lay in a square room, 15% for diagonal or herringbone patterns, and 20% for an irregular room. Always round up to whole boxes and keep the spares.
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The calculation
- Area. Length times width for each rectangle, added together.
- Add wastage. 10% for a straightforward room, more for complicated layouts.
- Divide by coverage per box. The figure printed on the packaging.
- Round up. Always up. You cannot buy nine tenths of a box.
A 20 square metre room at 10% wastage needs 22 square metres of material. At 2.2 square metres per box that is exactly 10 boxes. The same room in herringbone needs 24, which is 11 boxes.
Why wastage varies so much
| Situation | Allowance |
|---|---|
| Large plain rectangle, few cuts | 5% |
| Straight lay, simple room | 10% |
| Diagonal lay | 15% |
| Alcoves, bay windows, several doorways | 15% |
| Herringbone or chevron | 20% |
| Very irregular or many obstacles | 20% or more |
Diagonal and herringbone patterns waste more because every board meeting a wall needs an angled cut, and the offcut is rarely usable elsewhere. Large-format tiles waste more than small ones for the same reason: a cut discards more material.
If you are laying it yourself for the first time, add a little more. Practice costs material.
Buy a spare box and keep it
This is the advice most often ignored and most often regretted.
Flooring and tiles are made in batches, and shade varies between them. A replacement bought two years later will be visibly different even if the product code matches. If the line has been discontinued, it cannot be matched at all.
One spare box turns a damaged board into a twenty minute job. Without one it becomes a choice between an obvious patch and relaying the room.
Measuring properly
- Measure at the widest point. Rooms are rarely square, and you need the material to reach the far corner.
- Split odd shapes into rectangles and add the areas. An L-shape is two.
- Include doorways and alcoves you intend to floor.
- Measure twice. A mistake here is discovered at the checkout at best, mid-installation at worst.
- Do not subtract small obstacles like a kitchen island or a hearth. The saving is small and the offcuts rarely reusable.
What else you need
- Underlay for laminate and engineered wood. Same area, and you can skip the wastage allowance since it cuts without pattern matching.
- Adhesive or grout for tiles, quantities on the packaging and dependent on tile size and spacing.
- Beading or trim around the edges, measured by perimeter rather than area. The figure is above.
- Threshold strips for each doorway.
- Expansion gap around the perimeter for floating floors, usually 10 to 12 mm, covered by the skirting or beading.
Let it acclimatise
Wood and laminate expand and contract with humidity. Manufacturers generally ask for the boxes to sit flat in the room for 48 hours before laying, so the material reaches the temperature and humidity it will live at.
Skipping this is a common cause of gaps opening or boards buckling months later, and it is usually enough to void the warranty.
Frequently asked questions
How many boxes of flooring do I need?
Divide the room area by the coverage stated on the box, add a wastage allowance for offcuts, then round up to whole boxes. A 20 square metre room with boxes covering 2.2 square metres each needs 10 boxes at 10% wastage, not 9.
How much wastage should I allow?
10% for a straight lay in a simple rectangular room, 15% for diagonal layouts or rooms with alcoves and doorways, and 20% for herringbone, chevron or very irregular spaces. Large-format tiles waste more than small ones because each cut discards more material.
Should I buy extra beyond the wastage?
Buy one spare box and keep it. Batches vary in shade, and a discontinued line cannot be matched at all. Replacing a few damaged boards years later is trivial with a spare box and close to impossible without one.
How do I measure an L-shaped room?
Split it into rectangles, work out each area, and add them. The tool lets you add as many sections as you need. Measure at the widest points and include any alcoves or bay windows you intend to floor.
Does this include underlay and trim?
The area figure applies to underlay as well, though underlay usually needs no wastage allowance since it can be cut without pattern matching. Skirting and trim are measured by the room perimeter, which is shown alongside.