How Much Plaster Do I Need? Bags of Skim and Bonding Coat
A bag of plaster covers an area that depends on how thick you spread it. 16.2 m² of wall takes 2 bags of 25 kg of finishing plaster at 2 mm, with 10% extra. The plaster calculator works it out for your room.
Bags for each area
With 10% extra: finishing plaster at 2 mm, bonding coat on a wall at 11 mm, and bonding coat on a ceiling at 8 mm.
| Area | Finishing plaster, 2 mm | Bonding coat, wall, 11 mm | Bonding coat, ceiling, 8 mm |
|---|---|---|---|
| 10 m² | 2 | 4 | 4 |
| 20 m² | 3 | 8 | 7 |
| 30 m² | 4 | 12 | 10 |
| 40 m² | 5 | 16 | 13 |
| 60 m² | 7 | 24 | 19 |
| 80 m² | 9 | 32 | 26 |
How the thickness changes the bags
For 16.2 m² of finishing plaster:
| Thickness | Covered by one bag | Bags |
|---|---|---|
| 1.5 mm | 13.3 m² | 2 |
| 2 mm | 10.0 m² | 2 |
| 3 mm | 6.7 m² | 3 |
| 5 mm | 4.0 m² | 5 |
The coats
- Bonding coat. A thick base coat of 8 to 11 mm that levels a rough or uneven wall.
- Finishing plaster. The thin skim of about 2 mm that you trowel smooth and paint.
- On plasterboard. A skim coat of finishing plaster goes straight onto the board, with the joints taped.
Getting the amount right
- Measure the walls and the ceiling and take off the doors and the windows.
- Use the coverage on the bag you buy: the figures here are for the common 25 kg bags of finishing plaster and bonding coat.
- Add 10% for waste, and a little more if the wall is very uneven or absorbent.
- Mix small batches: plaster starts to set in less than an hour.
See also the plasterboard calculator and the paint calculator. These are estimates: check the coverage on the bag.
Frequently asked questions
How much plaster do I need?
Divide the area by the coverage of a bag at your thickness: 16.2 m² at 2 mm takes 2 bags of 25 kg of finishing plaster, with 10% extra.
How far does a bag of finishing plaster go?
About 10 m² at 2 mm for a 25 kg bag. It halves if you put it on twice as thick.
How far does a bag of bonding coat go?
About 2.75 m² on a wall at 11 mm, and 3.50 m² on a ceiling at 8 mm.
How thick should a skim coat be?
About 2 mm. A thicker skim cracks as it dries, and a thinner one is hard to trowel flat.
Does the type of plaster matter?
Yes. Hardwall, one-coat and lightweight plasters cover differently, so use the coverage on your bag, which this page does not give.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.