Working out drywall for a room
Board is bought by the sheet, so every calculation ends in a whole number of sheets and nothing smaller. Walls and ceilings are added together because they are hung from the same stack, then an allowance is added for offcuts, then the total is divided by whatever sheet size you have chosen to carry up the stairs.
- sheet area — 32 sq ft for 4 × 8, 40 for 4 × 10, 48 for 4 × 12
- 1.10 — the ten percent offcut allowance
- board area — what you actually hang, not the sheets you carry home
- 28–32 and 36–40 — screws per 4 × 8 sheet at 16 in centres on walls and 12 in on ceilings
- rate — 123–140 lb per 1,000 sq ft for conventional all-purpose compound, about 72 for a lightweight
Worked example: 800 sq ft of wall and 200 of ceiling
Twelve fewer sheets in the larger size, and twelve fewer sheets means fewer butt joints to hide. That is the real argument for long board, and the reason to check your stairwell before ordering it.
Why fastener spacing is not this calculator's decision
The screw figures here are estimating rates taken from manufacturer guidance, useful for filling a trolley. They are not a specification. Actual spacing is fixed by your local building code and by the board manufacturer's own schedule, and it changes with framing centres, board thickness, whether the assembly is fire or shear rated, and whether you are screwing to timber or steel. Look it up for your job. A calculator that told you otherwise would be overstepping.
Common mistakes
- Forgetting the ceiling. On a 12 by 16 room the ceiling is 192 sq ft, roughly six extra sheets, and it is the hardest part to go back for.
- Deducting every opening. Board is hung over openings and cut out afterwards. Deducting a door you then cut round leaves you a sheet short.
- Buying the sheet size you can lift rather than the one that fits. Two people and a panel lift beat a day of extra taping.
- Under-ordering compound. A three-coat finish uses far more than people expect, and running out mid-coat leaves a visible ridge where the wet edge dried.
When these numbers do not apply
- Level 5 finishes. A skim coat across the whole surface uses substantially more compound than the three-coat figure here.
- Steel framing. Different screws, different spacing, and the counts shift accordingly.
- Fire and acoustic assemblies. Double-layer board doubles the sheets and changes the fastener schedule entirely.
- Curved and vaulted work. Flexible board comes in smaller sheets and wastes far more than a flat ceiling.