What this calculator does
Sheet count is the wall area plus waste, divided by the area of one sheet, rounded up. A 5 by 4 metre room with 2.4 metre walls needs 36.60 m² of board, which at 10% waste is 40.26 m² and fourteen standard 1200 by 2400 sheets.
Larger sheets mean fewer sheets and fewer joints, which is the real benefit. The same room takes ten 1200 by 3600 sheets instead of fourteen small ones, cutting the number of joints to tape and sand by nearly a third. The trade is weight and handling: a 3600 sheet is awkward for one person.
The formula
The wall area is the room perimeter multiplied by the height, less a standard deduction for each door and window. The waste allowance is added, and the result divided by the sheet area and rounded up. Ceilings are not included, since they are usually boarded separately and often with a different thickness.
| Term | Meaning |
|---|---|
| Plasterboard | Also called drywall, gypsum board or by trade names. Sold in fixed sheet sizes. |
| Waste allowance | Extra for offcuts around openings and at corners. 10% is typical. |
| Joints | Where sheets meet, needing tape and compound. Fewer, larger sheets means fewer joints. |
| Sheet area | 2.88 m² for a 1200 × 2400 sheet, the most common size. |
The inputs explained
| Field | What to enter |
|---|---|
| Room length (m) | Room length in metres. |
| Room width (m) | Room width in metres. |
| Wall height (m) | Wall height. |
| Doors | Number of doors, deducted at a standard size. |
| Windows | Number of windows. |
| Sheet size | Sheet size. Larger sheets mean fewer joints but are heavier to handle. |
| Waste allowance (%) | Waste allowance. 10% suits a straightforward room. |
When to use it
Ordering board for a room
Sheets are bought whole, so the count is what the merchant needs.
Choosing a sheet size
Larger sheets reduce joints and finishing time, at the cost of handling difficulty.
Estimating a fit-out
Board is usually the largest single material item in an internal fit-out.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How many sheets in each size?
The same room boarded with three sheet sizes.
| Sheet size | Sheets needed | With waste allowance | Spare coverage left over |
|---|---|---|---|
| 1200 × 2400 mm | 14 | 40.26 m² | 0.06 m² |
| 1200 × 3000 mm | 12 | 40.26 m² | 2.94 m² |
| 1200 × 3600 mm | 10 | 40.26 m² | 2.94 m² |
Questions
What size plasterboard should I use?
The largest you can handle safely. Fewer sheets means fewer joints to tape, fill and sand, which is the slow part of the job. A 1200 by 3600 sheet weighs around 30 kg though, so it is a two-person lift and awkward on stairs.
How much waste should I allow?
Around 10% for a straightforward rectangular room. Increase it for rooms with many openings, angled walls or a lot of short runs, where offcuts are less likely to be reusable elsewhere.
Should I deduct for doors and windows?
For an accurate count, yes, and this does so automatically. On a small room the deduction is worth a sheet or two. Some fitters deliberately board over openings and cut them out afterwards, which wastes material but gives cleaner reveals.
Does this include the ceiling?
No, walls only. Ceilings are usually boarded separately, often with a thicker or sag-resistant sheet, and the area is simply the room length times the width. Add that separately if you are boarding both.
For painting the finished walls, see the paint calculator. For the framing behind them, see the wall stud calculator.