Repairs
Drywall Calculator
Find sheet counts, screws, joint tape, and compound for any room, with waste allowance included.
Your answer
Use moisture-resistant board in bathrooms and fire-rated board where building regulations require it.
Working out sheet counts
Drywall estimating is area divided by sheet size with a waste allowance, but the useful detail is which openings to deduct. Deduct doors and windows; ignore sockets, switches, and small service penetrations, because the cut-outs become waste rather than usable board.
Ten per cent waste is realistic for a plain rectangular room. Add more where there are many angles, a stairwell, or sloping ceilings, where whole sheets frequently produce a single usable piece.
Choosing the sheet size
Longer boards mean fewer joints, and joints are the slow, skilled part of the job. A 12 ft board across a 12 ft wall eliminates a butt joint entirely — butt joints are the hardest to hide because they have no tapered edge to bed the tape into. Against that, long boards are heavy and awkward for one person.
| Board type | Use | Note |
|---|---|---|
| Standard | General walls and ceilings | Cheapest, 12.5 mm typical |
| Moisture resistant | Bathrooms, utility, kitchens | Not a substitute for tanking in a shower |
| Fire rated | Garages, ceilings under habitable rooms | Often a building regulation requirement |
| Acoustic / high density | Party walls, home offices | Noticeably heavier to lift |
| Impact resistant | Hallways, children's rooms | Resists knocks and dents |
Fixings, tape, and compound
- Screws roughly every 300 mm on ceilings, 400 mm on walls, 12 mm in from any edge.
- Paper tape for flat joints, mesh for speed, and metal-reinforced tape on external corners.
- Three coats of compound: bedding, filling, and a wide skim, each sanded lightly.
- Around 0.25 kg of compound per square metre of board for a taped and filled finish.
Why more screws makes a weaker wall
A drywall screw grips through the paper face, not the crumbly gypsum core. Driven a fraction too deep it tears the paper and holds almost nothing. A depth-setting nose cone on the driver is a small purchase that fixes this permanently.
Common mistakes
- Butting boards tightly together instead of leaving a hairline gap for movement.
- Running boards vertically on walls, which doubles the awkward joint length.
- Over-driving screws until the paper tears around every head.
- Applying a thick second coat instead of two thin ones, causing cracking as it dries.
- Sanding aggressively and scuffing the paper face, which then shows through paint.
How many drywall sheets do I need for a room?
Total wall and ceiling area divided by the sheet area, plus about 10% for waste. A 4 by 8 ft sheet covers 32 sq ft; a 1200 by 2400 mm sheet covers 2.88 m².
How many screws per sheet?
Roughly 32 to 36 screws per 4 by 8 sheet on walls at 400 mm spacing, and closer to 45 on ceilings at 300 mm spacing.
How much joint compound will I use?
About 0.25 kg per square metre for a three-coat taped finish, or roughly one 20 kg bucket per 60-70 m² of board.
Should boards run horizontally or vertically?
Horizontal on walls in most cases: it puts the long joint at a comfortable working height and reduces total joint length by about 25%.
Last reviewed February 2026