Drywall Calculator — Sheets, Screws and Mud
Enter the room and get a sheet count with 10% for cuts, plus the screws and joint compound to go with it.
About the Drywall Calculator
Drywall maths is simple until you account for cuts, and cuts are where the waste lives. Ten percent is the standard allowance for a normal room with a door and a window. This also gives the screw count and joint compound, because those are the two things people forget until they are already covered in dust.
How to use it
- Measure the perimeter of the room and the wall height.
- Enter the ceiling area if you are boarding the ceiling too.
- Pick your sheet size — longer sheets mean fewer seams to finish.
- The 10% waste allowance is already included in the sheet count.
The formula
Wall area = perimeter × height
Sheets = (wall + ceiling) × 1.10 ÷ sheet area
A 4×8 sheet is 32 sq ft, 4×10 is 40, and 4×12 is 48. Longer sheets cost more per sheet but leave fewer butt joints, which are the hardest seams to finish invisibly.
Worked examples
| Room | Ceiling ht | Wall area | Ceiling | Total +10% | 4x8 sheets |
|---|---|---|---|---|---|
| 12 × 12 | 8 ft | 384 sq ft | 144 sq ft | 581 sq ft | 19 |
| 10 × 12 | 8 ft | 352 sq ft | 120 sq ft | 519 sq ft | 17 |
| 16 × 20 | 8 ft | 576 sq ft | 320 sq ft | 986 sq ft | 31 |
| Garage 20 × 20 | 8 ft | 640 sq ft | 400 sq ft | 1,144 sq ft | 36 |
Ceilings are worth pricing in 4×12 sheets. Fewer butt joints overhead is worth real money in finishing time, and butt joints on a ceiling are the ones that show under raking light.
Common mistakes
- Not subtracting anything, then not adding waste either. These two errors cancel out only by luck. Add 10% and ignore openings — the offcuts from around a door are rarely reusable.
- Using the wrong board in wet areas. Bathrooms and kitchens need moisture-resistant or cement board behind tile. Standard drywall fails there.
- Hanging sheets vertically on walls. Horizontal hanging puts the seam at a comfortable height and creates less total seam length to finish.
- Under-buying joint compound. Three coats over every seam and screw uses far more than expected — roughly 0.053 lb per square foot of board.
Terms explained
- Butt joint
- Where two un-tapered sheet ends meet. Harder to hide than a tapered edge, so plan the layout to minimise them.
- Tapered edge
- The long edges of a sheet, slightly recessed so tape and compound finish flush.
- Mud
- Joint compound. Sold pre-mixed in buckets or as a powder you mix — powder sets harder and faster.
- Level 5 finish
- A skim coat over the whole surface. Needed under gloss paint or strong raking light, where lesser finishes show every seam.
Common questions
- How many sheets of drywall do I need for a 12x12 room?
- About 19 sheets of 4×8, covering 384 sq ft of wall plus a 144 sq ft ceiling with 10% waste.
- How many square feet is a sheet of drywall?
- A 4×8 sheet is 32 sq ft, a 4×10 is 40 sq ft, and a 4×12 is 48 sq ft.
- How many screws per sheet of drywall?
- About 32 for walls at 16-inch stud spacing. Ceilings need more, around 36 to 40, because gravity is working against you.
- How much joint compound do I need?
- Roughly 0.053 lb per square foot of drywall for three coats — about 5 lb per 100 sq ft.
- Should drywall be hung horizontally or vertically?
- Horizontally on walls in residential work. It puts the seam at a workable height and reduces total seam length.
- What thickness of drywall should I use?
- Half-inch for walls and most ceilings. Five-eighths where fire rating is required, such as a garage sharing a wall with the house.
- How much waste should I allow for drywall?
- Ten percent for a typical room. Go to 15% if the room has many openings, angles or a vaulted ceiling.