Case 1
- Wall and ceiling area (sq ft)
- 640sq ft
- Area of one sheet (sq ft)
- 32sq ft
- Waste allowance
- 10%
22sheets
Open with these valuesDrywall Calculator
22sheets
Result: 22 sheetsWall and ceiling area divided by the area of one sheet, times the waste factor, rounded up. A 12 × 16 ft room with 8 ft walls is 640 sq ft, so 20 sheets of 4 × 8 ft, or 22 with a 10 % allowance for cuts. Sheet size is a field here, not a constant: 4 × 10 is 40 sq ft, 4 × 12 is 48.
The numbers at a glance
Held fixed: Wall and ceiling area (sq ft) 640.0 sq ft, Area of one sheet (sq ft) 32.0 sq ft.
| Waste allowance (%) | Result (sheets) |
|---|---|
| 4 | 21 |
| 6 | 22 |
| 8 | 22 |
| 10Your value | 22 |
| 12 | 23 |
| 14 | 23 |
| 16 | 24 |
Worked examples
Case 2
- Wall and ceiling area (sq ft)
- 1000sq ft
- Area of one sheet (sq ft)
- 32sq ft
- Waste allowance
- 0%
32sheets
Open with these valuesCase 3
- Wall and ceiling area (sq ft)
- 300sq ft
- Area of one sheet (sq ft)
- 48sq ft
- Waste allowance
- 0%
7sheets
Open with these valuesHow it's calculated
sheets = ⌈area ÷ sheet area × (1 + waste)⌉
- StepAdd the areas: width × length for the ceiling, (width + length) × 2 × height for the walls.
- StepEnter one sheet's area: 32 sq ft for 4 × 8 ft, 40 for 4 × 10, 48 for 4 × 12.
- StepSet the waste allowance — 10 % is the usual trade figure for cuts and breakage.
- ResultThe count rounds up to whole sheets; order tape and compound against the same area.
What this number means
Width of the room x Length of the room = Ceiling area. (Width + Length) x 2 x Height of the room = Wall area. For example: a 12' x 16' x 8' room has a wall/ceiling area of 640 sq. ft.
What the maker's table says about mud and tape
Georgia-Pacific's estimating table pairs 100 to 200 sq ft of board with a 12 lb pail of all-purpose joint compound and two 60 ft rolls of tape, 500 sq ft with a 48 lb carton and one 250 ft roll, and 800 sq ft with a 61.7 lb pail and two 250 ft rolls.
Sheet size is a field, not a hidden constant
The reference table gives the six panel sizes the maker publishes, from 32 sq ft up to 64. A German gypsum board of 1250 × 2000 mm is 2.5 m², which is 26.9 sq ft — type that in and the count follows the same rule.
The waste allowance is trade practice, not a rate
Both published tables list bare coverage with no allowance at all, which is why every test case behind this page runs at 0 %. The 10 % default is the common rule of thumb for cuts and broken corners, not a figure anyone measured.
The allowance goes on before the rounding
640 sq ft of 4 × 8 ft board is 20 sheets, and 10 % on top makes 22. Round to 20 first and add the 10 % afterwards and you land on 22 as well here, but at 1000 sq ft the two orders differ — apply the allowance first and round once.
Commonly misread
I measured the floor, so I entered 192 sq ft for a 12 × 16 room.
That is the ceiling alone. The walls of an 8 ft room add (12 + 16) × 2 × 8 = 448 sq ft, so the board area is 640 sq ft.
I put the sheet size in as 4 by 8 in the second field.
The field wants one number, the area of a sheet in square feet. A 4 × 8 ft sheet is 32; the table above lists the other five sizes.
Sheets are the whole order, so I only bought board.
Every joint needs tape and three coats of compound. The maker's table puts a 61.7 lb pail and two 250 ft rolls on 800 sq ft of board.
Reference table
| Panel size | One panel covers | Six panels cover |
|---|---|---|
| 4 ft × 8 ft | 32 sq ft | 192 sq ft |
| 4 ft × 9 ft | 36 sq ft | 216 sq ft |
| 4 ft × 10 ft | 40 sq ft | 240 sq ft |
| 4 ft × 12 ft | 48 sq ft | 288 sq ft |
| 4 ft × 14 ft | 56 sq ft | 336 sq ft |
| 4 ft × 16 ft | 64 sq ft | 384 sq ft |
Questions
How many sheets of drywall do I need?
Divide the wall and ceiling area by the area of one sheet, multiply by the waste factor, then round up. A 640 sq ft room with 4 × 8 ft sheets, each 32 sq ft, needs 640 ÷ 32 × 1.10, which is 22 sheets at 10 % waste.
What size is a sheet of drywall?
Sheets are 4 ft wide, and the maker behind this page publishes lengths of 8, 9, 10, 12, 14 and 16 ft — that is 32 to 64 sq ft of coverage. The 4 × 8 ft sheet is the one most homeowners can carry and cut alone.
How much joint compound and tape will it take?
The maker's estimating table gives a 12 lb pail and two 60 ft rolls of tape for 100 to 200 sq ft of board, a 48 lb carton and one 250 ft roll for 500 sq ft, and a 61.7 lb pail with two 250 ft rolls for 800 sq ft. Those are amounts to buy for a three-coat finish, not a measured usage rate.
How much waste should I add?
10 % is the common allowance for cuts, offcuts and broken corners, and it is what this page defaults to. It is a trade habit rather than a published rate — the coverage tables the cases come from carry no allowance at all, so set the field to 0 if you want the bare count.
Does the count subtract doors and windows?
No. Enter the net area yourself if the openings are large, and keep in mind that the board around a door still gets cut from a full sheet. For an ordinary door and one window most estimators leave the area in and let the waste allowance cover the offcuts.
Sources and last check
Information, not professional advice.