Two things no other plasterboard calculator tells you
1. What a sheet weighs
A 2400 × 1200 sheet is 2.88 square metres, so the density does the rest:
| Board | Roughly | A 2400 × 1200 sheet |
|---|---|---|
| 12.5mm standard | 9.5 kg/m² | about 27kg |
| 12.5mm fire | 11.5 kg/m² | about 33kg |
| 15mm fire | — | nearer 38kg |
| Acoustic | Denser again | No published figure here rather than a guess |
That is a two-man lift by any sensible measure. It is why boards come banded in pairs, why a ceiling wants a board lifter rather than a second person and optimism, and why the answer to "can we get these up the stairs" is worth working out before the pack arrives on a pallet at the end of the drive.
Nobody prints it. So it sits next to the board picker on this tool rather than in the results, because it should change what you choose, not tell you afterwards what you already committed to.
One thing that catches people: fire board is heavier than standard at the same thickness. The fire performance comes from what is in the core, and the core is denser. Acoustic board is denser still, because mass is the entire mechanism by which it stops sound.
2. How many metres of joint there are
Scrim tape and jointing compound are bought by the metre, and nobody works out the metres. Everybody buys a roll and hopes, or buys three and has two left.
It is arithmetic. Boards on a wall produce a predictable length of joint: one vertical for every board edge that meets another, plus a horizontal right across the wall for every course above the first.
A 6m wall at 2.4m high in 2400 × 1200 board is five columns, so four vertical joints, so 9.6 metres. No horizontals, because one course does it. Change to 1800 × 900 board and it more than doubles.
It is an estimate of a sensible layout rather than a measurement of your setting-out, and the tool says so. It is still a great deal better than guessing.
Skim and tape are different orders
Not two words for the same job.
Skimming puts plaster over the whole face: joints scrimmed first, then two coats of multi finish across everything. Material is driven by area.
Taping and jointing puts compound along the joints only, feathered out, and the board face is left as it is. Material is driven by joint length.
Those are completely different numbers off completely different inputs, which is why the tool asks which rather than giving you both and letting you sort it out at the merchant.
The horizontal joint always shows
If a wall is taller than the board, there is a horizontal joint straight across it. And that joint shows.
Not because it is worse work, but because it runs across the direction light travels down a wall. Any side light from a window or a wall light catches its whole length at once, and a vertical joint simply does not get lit that way.
A 2700 or 3000 board removes it entirely on most rooms. Heavier per sheet: the tool will tell you by how much, and worth it.
Ceilings take more screws
About 40 per square metre against 30 on a wall, because a ceiling board is being held against gravity rather than pressed flat against a stud.
A popped screw on a wall is a blemish. On a ceiling it is the start of a crack, and it is directly above where you will be standing when you notice it.
Thickness, fire rating and acoustics are specified for you
It does not decide board thickness, fire rating or acoustic performance. Those are specified: by Building Regulations, by a designer, or by what the room is, and they are not choices a calculator should make.
Next to it: stud walls, which produce the area this needs, and render and plaster.
Common questions
How much does a sheet of plasterboard weigh?
A 2400 × 1200 sheet of 12.5mm standard is about 27kg. In 15mm fire board it is nearer 38kg. That is not a one-person lift, it is why boards come banded in pairs, and it is the entire reason a ceiling wants a board lifter rather than a second person and optimism.
Is fire board heavier than standard board?
Yes, and at the same thickness. Fire-rated 12.5mm is around 11.5 kg/m² against 9.5 for standard, because the extra fire performance comes from additives in the core. People carrying it notice long before anybody explains it.
How much scrim tape do I need?
Work out the joint length, which is what nobody does. Boards produce a predictable amount: one vertical joint per board edge that meets another, plus a horizontal right across for every course above the first. A 6m by 2.4m wall in 2400 × 1200 board is about 9.6m of joint. It is two minutes of arithmetic and it is why everybody guesses a roll.
How many screws per board?
Roughly 30 per square metre on a wall and 40 on a ceiling. A ceiling takes more because the board is being held against gravity rather than pressed flat against a stud, and a screw that pops on a wall is a blemish while one on a ceiling is a crack.
Skim or tape and joint?
They are different material lists, not two names for the same thing. Skimming needs plaster over the whole face, at roughly a 25kg bag per 5m² across two coats, with the joints scrimmed first. Taping needs jointing compound along the joints only. Ordering the wrong one is a wasted trip.
Should I use a taller board?
If the wall is over 2.4m, seriously consider it. A 2700 or 3000 board removes the horizontal joint entirely, and a horizontal joint across the middle of a wall always shows, because it catches side light along its whole length in a way a vertical joint does not.