PreConstruct AICanadian drawings for commercial work are usually in millimetres, and a partition 30 m long and 2.7 m high is easy to measure. Board, though, is still sold in imperial sheets — so the takeoff runs in square metres and the order in sheets. The conversions are simple once, and then they are the same every job.
Sheet sizes in square metres
| Sheet | Millimetres | m² a sheet | Sheets per 100 m² |
|---|---|---|---|
| 4 × 8 ft | 1219 × 2438 | 2.97 | 33.6 |
| 4 × 9 ft | 1219 × 2743 | 3.34 | 29.9 |
| 4 × 10 ft | 1219 × 3048 | 3.72 | 26.9 |
| 4 × 12 ft | 1219 × 3658 | 4.46 | 22.4 |
Thicknesses are the imperial ones in millimetres: 12.7 mm (½ in) and 15.9 mm (⅝ in), usually written 13 mm and 16 mm on drawings. Type X fire-rated board is almost always 15.9 mm.
Board area
For a partition: length × height × faces × layers, less the openings on each face. For a ceiling: length × width × layers. Then add a waste allowance — commonly 5 to 15 per cent depending on how cut-up the walls are — and divide by the sheet area, rounding up.
Finishing rates per square metre
Converted from the common imperial starting rates. They are starting points, not rules — the level of finish and your finishers change them.
| Item | Imperial rate | Per m² of board |
|---|---|---|
| Screws (walls, studs at 400 mm) | about 32 per 4 × 8 sheet | about 10.8 |
| Paper joint tape | about 370 LF per 1,000 SF | about 1.21 m |
| Ready-mixed all-purpose compound | about 10 US gal per 1,000 SF | about 0.41 L |
A worked example
A corridor partition 30 m long and 2.7 m high, one layer each side, with two doors 900 × 2100 mm:
- Wall:
30 × 2.7 × 2 faces = 162 m² - Doors:
0.9 × 2.1 = 1.89 m², × 2 doors × 2 faces = 7.56 m² - Board:
162 − 7.56 = 154.44 m² - With 10 per cent waste:
154.44 × 1.10 = 169.88 m²÷ 2.97 m² = 57.2 → 58 sheets of 4 × 8 - Screws:
58 × 32 = 1,856 - Tape:
154.44 × 1.21 ≈ 187 m - Compound:
154.44 × 0.41 ≈ 63 L— about four 17 L pails
At 2.7 m, 4 × 8 sheets hung horizontally leave a strip at the top; many crews hang 4 × 9 or 4 × 10 to avoid it. The sheet choice changes the count, so check how the job will be hung.
Doing it on the drawings
PreConstruct AI shows quantities in imperial, metric or both — the company's choice. You click along the walls on a metric or imperial drawing, pick the wall type, and board comes out in sheets with the square metres and the arithmetic beside it, at your own waste and rates.