Drywall Sheets Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/8/2026
The number of drywall sheets is calculated by dividing the surface to cover (plus the offcut margin) by the surface of a standard sheet (2.50 × 1.20 m, or 3 m²). For 20 m² with a 10% margin, you need 8 sheets.
Explanation
The most common standard size for plasterboard sheets (commonly called 'drywall' or 'plaster board') is 2.50 meters long by 1.20 meters wide, or 3 m² per sheet. Other sizes exist, with lengths up to 3.60 meters to limit the number of joints on tall walls, but the 2.50 × 1.20 m size remains the most common in distribution for typical residential use (standard ceiling height). Calculating the number of sheets needed follows the same principle as for tiling or flooring: divide the total surface to cover, increased by an offcut margin, by the surface of one sheet, then round up to the next whole sheet. The offcut margin depends on the room's layout: a simple rectangular surface, with no openings, needs a modest margin (around 10%), while a room with many cuts (doors, windows, non-rectangular corners, duct passages) generates more offcuts and warrants a larger margin. A practical point to anticipate: for a partition built on both sides of a metal frame, the number of sheets calculated here must be doubled, since this calculator only covers one side.
Example: 20 m² to cover, 10% offcut margin
Inputs
Surface to cover: 20 m². Offcut margin: 10%.
Calculation
Surface with margin = 20 × 1.10 = 22 m². Number of sheets = 22 ÷ 3 ≈ 7.33, rounded up to 8 sheets.
Result
You need to buy 8 standard-size drywall sheets for this surface.
Frequently asked questions
Should the number of sheets be doubled for a partition wall?
Yes, if the partition must be covered on both sides (the most common case for an interior dividing wall): this calculator gives the number of sheets for one side only. For lining an existing wall (only one side covered), the result calculated here is sufficient as is.
Why should a larger offcut margin be planned with many cuts?
Because each cut around a door, window, or non-right-angle corner generates sheet offcuts that generally cannot be reused elsewhere on the job, unlike a simple installation on a continuous rectangular surface. A complex room, with many openings, can easily warrant a margin of 15 to 20% rather than the usual 10%.
Are there other sheet sizes besides 2.50 × 1.20 m?
Yes, plasterboard sheets are available in a range of lengths from 2 to 3.60 meters, with widths of 60, 90, or 120 cm depending on the manufacturer and use (ceilings, curved partitions, tall walls). The 2.50 × 1.20 m size nonetheless remains the most used for standard residential use, which is why it is the default reference in this calculator.