Plastering calculator
Gypsum and lime-cement plaster by room: walls, ceilings, reveals, primer, profiles, skim coat and paint
How the calculation works
Enter rooms (draw the outline with a finger or mouse, then enter the wall lengths), wall height, which walls and ceilings you plaster, and doors and windows with reveal depth. Choose the plaster type and thickness for walls and ceiling; consumption is scaled with thickness only within the product's applicable range. The calculator adds up the areas, groups the same product before rounding to bags, and adds primer, corner profiles and optional skim coat and paint.
Formula and assumptions
Wall area = length × height − openings + reveals. Door reveal = (2 × height + width) × depth, window reveal = (2 × height + 2 × width) × depth. Plaster (kg) = area × consumption at reference thickness × (thickness ÷ reference thickness). Bags = ⌈kg × (1 + reserve) ÷ bag size⌉.
Worked example
Room 4 × 3 m, height 2.6 m: walls 36.4 m², door and window −3.29 m², reveals +1.47 m² = 34.59 m². Gypsum plaster 15 mm at 10 kg/m² per 10 mm gives 15 kg/m²: 34.59 × 15 = 518.8 kg, with a 5 % reserve = 544.7 kg, so 19 bags of 30 kg.
More worked examples
- Walls 50 m², gypsum plaster 10 mm (10 kg/m²): 500 kg, with a 5 % reserve = 525 kg, 18 bags of 30 kg.
- Ceiling 12 m² at 10 mm and walls 36.4 m² at 15 mm of the same plaster: 120 + 546 = 666 kg in one line, 23 bags of 30 kg.
Gypsum plaster consumption (10 kg/m² at 10 mm) by thickness
| Thickness (mm) | kg/m² | m² per 30 kg bag |
|---|---|---|
| 8 | 8 | 3.8 |
| 10 | 10 | 3.0 |
| 15 | 15 | 2.0 |
| 20 | 20 | 1.5 |
| 25 | 25 | 1.2 |
What affects real consumption
- Layer thickness and product consumption set the amount of plaster; outside the applicable range no result is given.
- Openings are deducted and reveals added; small openings can optionally be left in.
- The same product on walls and ceiling is rounded to bags only once.
Common mistakes
- Thickness outside the product's applicable range.
- Forgetting the reveals around doors and windows.
- Rounding the same product separately for walls and ceiling.
Frequently asked questions
Why does the calculator refuse a thickness outside the applicable range?
Consumption is linear only within the range the manufacturer allows. A thicker or thinner layer needs another product or method, so the calculation stops instead of giving an unreliable figure.
Are the default consumptions manufacturer data?
No. They are typical values that you should replace with the data sheet of the product you use.