How to calculate the number of boards/sheets from an area — and why the waste allowance is never a fixed percentage, but depends on the room, the pattern, and the piece length.
Introduction
When an area is to be clad with boards or panels, the basic calculation is simple: divide the area by the area each item covers, and round up to whole items.
Example: 20 m² of floor with boards of 120 mm × 2400 mm. Area per board = 0.12 · 2.4 = 0.288 m². 20 / 0.288 ≈ 69.4 boards. With 10 % waste: 69.4 · 1.10 ≈ 76.4 → 77 boards.
Wastewater, aerated
Spilled water and grease make floors slippery, and falls are one of the most common workplace accidents in kitchens — that's why spillage is wiped up immediately.
- 01Straight runs in a rectangular room: low waste.
- 02Diagonal or herringbone: higher waste due to many cuts.
- 03Short pieces in a long room: more joints, more offcuts.
Indicative waste according to pattern
There is no standardised waste percentage — it depends on space, pattern and item length. The following are indicative experience intervals (industry practice, not standard figures); you must estimate the specific waste based on the task, and the supplier's own figures take precedence.
| Material / pattern | Guideline waste | Note |
|---|---|---|
| Floor boards, even run | ca. 5–8 % | Rectangular room, long boards |
| Floorboards, diagonally | ca. 10–15 % | Many cuts at the walls |
| Floor boards, herringbone | ca. 10–15 % | Short items, many adjustments |
| Gypsum boards | ca. 5–10 % | Depends on openings and room shape |
| Roof tiles / roof sheets | ca. 5 % | Plus broken and half bricks at edges |
| Facade cladding (clinker/trim) | ca. 8–12 % | Shorten at corners and openings |
The intervals are guidelines (industry practice, compiled 2026). Use the high end for small, divided rooms with many corners, and the low end for large, rectangular surfaces.
Covering width is not the raw measurement
Consumption is always calculated on the covering (effective) width — the width each piece actually covers when the adjacent piece is laid. For profiled boards, some of the raw dimension disappears into the joint or under the overlap.
| Clothing type | Covering width | Why |
|---|---|---|
| Notch and feather | Raw width minus the spring | The spring is hidden in the neighbour board |
| Cleat (overlap) | Raw width minus the overlap | Each board covers the one below |
| List covering (vertical) | Sub-board plus opening under the list | Dæk-mål = bræt + mellemrum |
| Ploughed boards / plaster | Modulmål (fx 900/1200 mm) | Edges meet — no overlap |
Always check the coverage width in the manufacturer's data sheet — it is stated as »coverage width« or »effective width«, and that's the figure you divide the room width by.
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