Plaster calculator (multi-finish)
Enter the wall or ceiling area in m² and the coat thickness in mm to see how many 25kg bags of multi-finish to buy.
Estimates only. Check the manufacturer's coverage rates.
How this is calculated
Multi-finish is a finishing plaster used for thin skim coats. The amount you need depends on the area, how thick the coat is and how much plaster each square metre takes per millimetre of thickness.
The formula is: plaster (kg) = area (m²) x thickness (mm) x kg per m² per mm x (1 + wastage / 100). The default coverage is 1 kg per m² per mm, a typical rule of thumb for finishing plaster, and the default wastage is 10% for mixing and droppings. The total is divided by 25 and rounded up to whole 25kg bags.
For example, 20 m² at 2 mm with 10% wastage is 20 x 2 x 1.0 x 1.1 = 44 kg, which rounds up to 2 bags.
To find the area of a wall, multiply its length by its height, add the walls together and take off large doors and windows. Products vary, so check the bag for its coverage and enter it in the coverage box. Multi-finish is meant for thin skim coats of a few millimetres; thicker coats normally use a backing plaster first.
- 1 kg per m² per mm is a typical rule of thumb for finishing plaster. Products vary, so check the bag.
Frequently asked questions
How much multi-finish do I need per m²?
A typical rule of thumb is 1 kg per m² for each millimetre of thickness, so about 2 kg per m² for a 2 mm skim. Products vary, so check the bag.
How thick should a skim coat be?
Multi-finish is meant for thin skim coats of a few millimetres. The calculator starts at 2 mm.
What if I need a thicker coat?
Thicker coats normally use a backing plaster, with a finishing plaster skimmed over the top.