How Many Bags of Plaster for a Flat: Gypsum or Lime-Cement
Short answer: for two rooms (5 × 4 m and 3.5 × 3.2 m, 2.6 m high) with doors and windows the walls have 77.46 m² and the ceilings 31.2 m². With gypsum plaster 15 mm on the walls and 10 mm on the ceiling that is 1474 kg, or 1548 kg with a 5 % allowance – 52 bags of 30 kg. If you plaster the walls with 15 mm of lime-cement plaster (about 14 kg/m² per cm), you need 43 bags of 40 kg for the walls and 11 bags of gypsum plaster for the ceilings. The plastering calculator works this out from the room plans.
Published:
What decides the number of bags
- Net area: walls minus doors and windows, plus the reveals around openings.
- Coat thickness – consumption grows linearly with thickness.
- The product's consumption per m² at a reference thickness and the bag size from the technical data sheet.
- An allowance for losses in mixing and application.
How to use the plastering calculator – step by step
- 1. Draw or enter each room and the wall height (2.6 m).
- 2. Add doors and windows with the reveal depth (12 cm for doors and 20 cm for windows in the example).
- 3. Mark which walls and ceilings you are plastering.
- 4. Choose the plaster and thickness for walls and ceiling; match consumption and bag size to the technical data sheet.
- 5. Optionally add primer, corner beads, skim coat and paint.
- 6. The calculator adds up the same product from all rooms before rounding to bags.
Example: two rooms, gypsum plaster
The walls of both rooms have 81.64 m² gross. Openings (two doors and two windows) take away 7.69 m², and reveals add 3.51 m², so the net area is 77.46 m². The ceilings have 31.2 m².
| Item | Calculation | To buy |
|---|---|---|
| Gypsum plaster, walls 15 mm | 77.46 m² × 15 kg/m² = 1162 kg | – |
| Gypsum plaster, ceilings 10 mm | 31.2 m² × 10 kg/m² = 312 kg | – |
| Gypsum plaster in total | 1474 kg + 5 % = 1548 kg | 52 bags of 30 kg |
| Primer 0.2 L/m² | 22.8 L with allowance | 5 cans of 5 L |
| Corner beads at openings | 21.5 m | 9 pcs of 3 m |
Gypsum or lime-cement plaster
The gypsum machine plaster in the example uses about 10 kg/m² at 10 mm, is applied 8–30 mm thick and, according to its data sheet, is also suitable for kitchens and bathrooms in homes. The lime-cement machine plaster uses about 14 kg/m² per cm, is applied at least 10 mm thick on walls, and the manufacturer also intends it for wet rooms.
For the same 77.46 m² of walls at 15 mm, lime-cement plaster needs 1627 kg, or 1708 kg with the allowance – 43 bags of 40 kg. More weight does not necessarily mean a higher price: compare the price per bag and the number of bags.
Most common mistakes
- Thickness estimated from the straightest wall – measure deviations with a straightedge and use the average thickness.
- Forgotten reveals: in the example they add 3.51 m².
- The same product rounded to bags separately for each room instead of once for the whole flat.
- One product's consumption applied to another – lime-cement and gypsum plaster differ in kg/m² and bag size.
- A thickness outside the product's range – the calculator then does not calculate the quantity.
Sources and assumptions
The consumption of gypsum plaster (10 kg/m² at 10 mm, 30 kg bag, 8–30 mm coat) and of lime-cement plaster (about 14 kg/m² per cm, 40 kg bag) are taken from the technical data sheets of the products in the example. Primer at 0.2 L/m², 3 m corner beads and a 5 % allowance are calculator defaults. Actual consumption depends on how straight the walls are and on the application method. These are typical values – the data on the pack or technical data sheet of the product you buy applies.
Plaster drying time before skim coat and paint
Lime-cement plaster typically dries about 1 day per mm of thickness (a 15 mm coat about 15 days), and gypsum plaster about 14 days at 10 mm. A concrete substrate must be dry before plastering, usually at least 4 weeks after pouring. These are typical values at about 20 °C; the product data sheet takes precedence. The work plan in a project uses your saved calculations to put plastering, skim coat and painting in order with dates.
Frequently asked questions
How many bags of plaster for a two-room flat?
For 77.46 m² of walls (15 mm) and 31.2 m² of ceilings (10 mm), gypsum plaster needs 1548 kg with the allowance – 52 bags of 30 kg.
Why does lime-cement plaster need more kilograms?
It is denser: about 14 kg/m² per cm against 10 kg/m² for gypsum. For the same walls that is 1708 kg, but in 40 kg bags, so 43 bags.
How many corner beads for doors and windows?
Beads go along the edges of openings: for the two doors and two windows in the example 21.5 m, i.e. 9 beads of 3 m.
How much primer before plastering?
The calculator counts 0.2 L/m² with a 5 % allowance: for 108.66 m² of walls and ceilings that is 22.8 L, i.e. 5 cans of 5 L. Check in the data sheet whether and how much primer your substrate needs.
Calculate yours: Plastering calculator