Skim coat calculator
A finishing skim coat is the thin layer that turns a rough wall into a smooth one ready for paint. The quantity depends on the wall area, the number of coats and how thick each coat is — and on walls that aren't straight it grows quickly.
Enter the room dimensions and the consumption printed on the bag; the calculator gives the kilograms and whole bags.
Your measurements
About 1.2 kg/m² for a thin coat of roughly 1 mm — check the bag.
Result
- Wall area
- 33.40 m²
- Skim coat needed
- 80 kg
- Bags to buy
- 4 pcs
Gypsum-based and ready-mixed polymer skim coats have different consumption — use the figure on the bag.
How the calculation works
- Wall area = 2 × (length + width) × height, minus doors and windows.
- Skim coat needed (kg) = wall area × number of coats × consumption per coat (kg/m²).
- Bags = kilograms ÷ bag size, rounded up.
Worked example
The walls of a 4 × 3 m room, 2.6 m high, have 33.4 m² once 3 m² of doors and windows are deducted. Two coats at 1.2 kg/m² each need 33.4 × 2 × 1.2 = 80 kg of skim coat, which is 4 bags of 25 kg (3.2 rounded up).
What the calculator assumes
- 1.2 kg/m² per coat corresponds to a thin layer of about 1 mm over straight plaster.
- Two coats are standard for a wall ready to paint; a third is applied only locally, on defects.
- The ceiling is not included — add length × width if you skim it too.
When to adjust the result
- On walls that are out of true by more than 2–3 mm, consumption rises sharply; a levelling plaster first can be cheaper.
- Gypsum-based and ready-mixed polymer products have different consumption — use the figure on the packaging.
- On clay walls or over old paint, the background needs special preparation or the skim coat will flake.
Frequently asked questions
How much skim coat per square metre?
Roughly 1–1.5 kg per square metre for each thin coat of about 1 mm. Two coats on a straight wall need around 2.4 kg/m²; uneven walls need more.
Do I need a primer before skimming?
Usually yes: a suitable primer controls the absorption of the background and helps adhesion. Which primer depends on the surface — the skim coat manufacturer specifies it.