Plaster Calculator
Enter the area, layer thickness and the consumption from the bag to get kilograms and bags.
The formula
Kilograms = area × thickness (mm) × consumption (kg/m² per mm). Gypsum mixes typically use 0.8–1.0 kg and cement-sand mixes 1.7–1.9 kg per m² per millimetre.
Worked example
40 m² of wall, an average 15 mm layer, gypsum mix at 0.9: 40 × 15 × 0.9 = 540 kg, which is 18 bags of 30 kg.
Finding the average layer thickness
Check the wall with a straightedge or a laser in several places, note the largest and smallest deviation, take the average and add 5 mm for the beads. The classic mistake is to plan for the thinnest spot: on a wavy wall the real consumption can be twice as high.
Gypsum or cement
| Criterion | Gypsum | Cement |
|---|---|---|
| Where it is used | Dry rooms | Facade, bathroom, plinth |
| Thickness in one pass | up to 30–50 mm | up to 20–30 mm |
| Working time | 30–50 min | 1–2 h |
| Under tiles in a wet area | Not all grades | Yes |
The maximum thickness per pass is on the bag. Exceeding it is the main cause of cracking and delamination.
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