Plastering calculator
Enter the wall and ceiling areas and choose the system — skim only, board and skim, or two-coat to masonry. The calculator returns bags per coat using typical coverage figures, so your quote and your merchant order match.
Pricing the job? Open EstiMate free and these quantities go straight onto the materials list with your prices.
How it works out the quantities
- 1Finishing plaster (multi-finish) covers about 10 m² per 25 kg bag at 2 mm; a re-skim uses one finish coat, board-and-skim the same over new plasterboard.
- 2Bonding coat covers about 2.5–3 m² per bag at 11 mm on masonry; hardwall about 3 m² per bag at 11 mm.
- 3Board finish is used over plasterboard where a thinner, faster set is wanted — around 11 m² per bag.
- 4Coverage drops on uneven walls; the waste field adds 10% by default.
Site tips before you order
- Count reveals, soffits and ceilings separately — a 'small room' is often 55–65 m² of plaster.
- PVA or a bonding agent on smooth or painted surfaces changes the spec; price it as a line.
- Beads, scrim and dust sheets aren't in the bag count — add them to the quote.
- Drying time between coats and before decorating goes on the programme, not in the price.
Common questions
How many m² does a bag of multi-finish cover?
About 10 m² at a 2 mm skim; less on rough backgrounds. The calculator uses that figure and adds your waste percentage.
How much plaster to skim a 4 m × 3 m room with a 2.4 m ceiling?
Walls (2 × (4 + 3) × 2.4) = 33.6 m², ceiling 12 m² — 45.6 m² total, about 5 bags of multi-finish with 10% waste.
What's the difference between bonding and hardwall?
Both are undercoat plasters for masonry. Bonding is for low-suction backgrounds (concrete, dense blocks, painted); hardwall for high-suction backgrounds like brick and aerated blocks.
Can I get a per-m² quote from this?
The calculator gives quantities; EstiMate's quote builder adds your labour rate per m² and learns it for next time.
Related calculators
Rendering calculator
Set the wall area, the number of coats and thickness, and the ratio for scratch and top coats. It returns ceme…
Paint coverage calculator
Enter the room size and ceiling height, deduct doors and windows, choose coats and the paint's coverage, and g…
Stud partition calculator
Enter the wall length and height and choose the stud centres. The calculator returns studs, noggins, plates, p…
Quantities are half the quote. EstiMate does the other half.
Drop the numbers into a priced, branded quote your client can accept online — free for your first three jobs a month.
Try EstiMate freeNo credit card · Free plan always available · Cancel anytime