Plaster calculator
A 25kg bag of Thistle Multi-Finish skims about 10 m² at 2 mm thick.
- Plaster needed
- 26.4 kg
- One bag covers
- 10.0 m²
- Area
- 9.6 m²
9.6 m² at 2 mm thick, plus 10% extra. One bag covers about 10 m² at this thickness.
For finishing (skim) plaster only. Bonding and backing plasters cover far less per bag.
Bags of plaster by area
At 2 mm thick with 10% extra.
| Area | Example | 25kg bags |
|---|---|---|
| 5 m² | Small wall | 1 |
| 10 m² | One wall of a bedroom | 2 |
| 15 m² | Small ceiling | 2 |
| 20 m² | Large ceiling | 3 |
| 35 m² | All walls of a bedroom | 4 |
| 50 m² | All walls of a living room | 6 |
How we calculate this
Jewson lists Thistle Multi-Finish at about 10 m² per 25kg bag at 2 mm. A thicker coat covers proportionally less, so 3 mm covers about two thirds as much.
We add extra for mixing waste and the plaster left on your tools, then round up to whole bags.
Questions people ask
How much does a bag of plaster cover?
A 25kg bag of Multi-Finish covers about 10 m² at 2 mm thick. Other plasters vary, so check the bag.
How thick should a skim coat be?
Usually about 2 mm, applied in two thin coats. Uneven walls may need a backing or bonding coat first, which is a different product.
How long does plaster last once mixed?
Not long. Mix only what you can apply before it starts to set, and check the working time on the bag. Unopened bags also have a use-by date, so don’t overbuy.
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