A standard sheet is 2440 by 1220 millimetres, which is 2.9768 square metres — the metric descendant of the eight by four foot sheet. Some suppliers stock a true metric 2400 by 1200 sheet at 2.88 square metres instead, and the two are close enough to be mistaken for each other and far enough apart to leave you a sheet short on a large job. The sheet size is therefore an input here rather than a constant.
Dividing area by sheet area gives the theoretical minimum, but a real deck of sheets is laid out in rows and columns and the offcuts are rarely reusable. Laying full sheets across a four metre span takes two sheets per row whatever the remainder, so the layout count is often a sheet or two higher than the area count. Both figures are shown, because the truth for a given job usually sits between them.
A 4 by 3 metre area is 12 square metres, which is 4.03 sheets on area and so 5 whole sheets. Laid out as full sheets it needs 2 across by 3 down, which is 6 sheets. A ten per cent allowance on the area figure gives 5 — still short of the layout count, which is why both matter.
The formula
area- Surface to be covered, in m²
sheet length, width- Sheet dimensions in mm; 2440 × 1220 is 2.9768 m²
layout count- Sheets across × sheets down, laying full sheets only
waste- Cutting allowance for openings, trims and unusable offcuts
How to use this calculator
- Enter the length and width of the surface you are sheeting.
- Confirm the sheet size — 2440 × 1220 and 2400 × 1200 are both common.
- Set the waste allowance for cuts, openings and unusable offcuts.
- The gauge shows sheets by area; the layout count and order are below.
Worked examples
A 4 × 3 m floor deck
The area is 12 m² and each 2440 × 1220 sheet covers 2.9768 m², so the area method gives 4.03 — 5 sheets. Laying full sheets means 2 across and 3 down, which is 6 sheets. Order 6.
Metric sheets are not the same
At 2400 × 1200 each sheet covers 2.88 m² rather than 2.9768, so the same 12 m² needs 4.17 sheets — 5 whole ones. On a fifty sheet order that difference is nearly two sheets.
How to read your score
Frequently asked questions
Why does the layout count come out higher than the area count?
Because sheets are rectangles and rooms rarely divide neatly by them. The area method assumes every offcut is reused somewhere, which is true on a plain floor deck and false as soon as there are openings, noggins or a fixed sheet direction. Use the layout count when the sheets must run one way.
Is 2440 × 1220 the same as eight by four feet?
Almost exactly. Eight feet is 2438.4 millimetres and four feet is 1219.2, so the metric sizes are rounded up by a millimetre or two. The genuinely different sheet is the true metric 2400 by 1200, which is 3.3 per cent smaller in area.
Which thickness should I use?
It depends on span and load rather than on area, so it does not change the sheet count. As a guide, 18 millimetres for a floor deck at 400 millimetre joist centres, 12 for wall sheathing and 9 or 11 for a roof deck with noggins. Thicker sheets are heavier to handle rather than automatically better.
How should I lay the sheets out?
With the long edge across the joists and the joints staggered between rows, so no two sheet ends meet on the same joist. Leave a two to three millimetre expansion gap around the perimeter and at sheet joints on a floor.
Should I allow more than ten per cent?
Yes if the surface has openings, a diagonal edge or a lot of trimming — fifteen per cent is safer there. On a plain rectangular deck with full sheets you may waste almost nothing, and the layout count already tells you the honest maximum.
Plywood sheet reference
| Area | 2440 × 1220 bare | +10% waste | 2400 × 1200 bare | +10% waste |
|---|---|---|---|---|
| 5 m² | 2 | 2 | 2 | 2 |
| 10 m² | 4 | 4 | 4 | 4 |
| 15 m² | 6 | 6 | 6 | 6 |
| 20 m² | 7 | 8 | 7 | 8 |
| 30 m² | 11 | 12 | 11 | 12 |
| 50 m² | 17 | 19 | 18 | 20 |
| 75 m² | 26 | 28 | 27 | 29 |
| 100 m² | 34 | 37 | 35 | 39 |
A 2440 × 1220 sheet is 2.9768 m²; a true metric 2400 × 1200 sheet is 2.88 m². Check a full-sheet layout as well.