Drywall Calculator
Sheets, screws, tape and compound for a room, minus the openings.
How it works
The area arithmetic is trivial; the reason estimates come out wrong is everything around it.
Openings only count when they are big. A door is worth subtracting — roughly 1.8 m² — and so is a decent window. Small windows are usually left in the calculation, because a sheet with a small hole cut in it is still a sheet you had to buy, and the offcut rarely lands anywhere useful.
Sheet count is the total area divided by the sheet area, rounded up, plus waste. Ten percent is right for a plain rectangular room and low if the room has dormers, angles or a lot of openings — every cut edge is a piece you cannot use elsewhere.
Screws go at roughly 300 mm centres on studs and 200 mm on ceilings, which works out around 32 per standard sheet on walls and closer to 40 on a ceiling. Buy by weight rather than by count: 1000 × 32 mm drywall screws is about 3.5 kg.
Compound is where amateurs under-buy by a wide margin. Three coats over every joint, plus every screw head three times, plus corner beads, comes to about 0.5 kg per square metre of board for a taped-and-jointed finish. A level 5 finish — a skim over the entire surface — roughly doubles it.
Ceilings take longer than everything else combined. Board them first, so the wall sheets hold the ceiling edges up, and use a lifter unless you have two friends who owe you something substantial.
Common questions
Should I board the ceiling first?
Yes. Ceiling sheets go up first and the wall sheets are then pushed up tight underneath them, which supports the ceiling edge and gives you a cleaner joint at the wall-ceiling junction.
Horizontal or vertical sheets?
Horizontal on a standard-height wall — it puts the long joint at waist height where it is easy to finish, and it produces less total joint length. Vertical is for walls taller than a sheet is long, and for fire-rated assemblies that specify it.
How much compound do I really need?
Around 0.5 kg per square metre of board for a normal taped finish over three coats. That is far more than most people expect. Buying the small tub twice costs more than buying the large one once.
What about dot-and-dab?
Adhesive instead of screws onto masonry, roughly one 25 kg bag per 5 m² of board. It is faster on solid walls and gives you no cavity for services, which is the usual reason not to.