Plaster calculator
Cement bags and sand for plastering — pick the surface (internal, external or ceiling) and the standard thickness and mix come with it. Uses the trade’s 1.33 dry-volume factor, so what you get is the material to order, not the wet volume on the wall.
Single coat over brickwork, finished for putty and paint.
Don’t know your plaster area?
It is roughly twice the internal wall area plus the ceilings — fiddly to measure by hand. Generate a floor plan for your plot and the materials card measures the plasterable surfaces off the validated plan and pre-fills this page.
Common questions
How much cement and sand for 100 m² of plaster?
For 12 mm internal plaster in 1:6, 100 m² takes roughly 7 bags of cement and 1.5 m³ (about 50 cft) of sand including 10% wastage. External 15 mm plaster in the richer 1:4 mix takes noticeably more cement for the same area — around 12 bags.
What plaster thickness should be used where?
12 mm on internal brick walls, 15 mm outside (up to 20 mm in two coats where the masonry is rough or needs a textured finish), and only 6 mm on RCC ceilings — thicker ceiling plaster tends to debond and fall.
Why is the dry volume more than the plaster thickness suggests?
Cement and sand lose volume once water is added and voids fill, so the trade multiplies the wet mortar volume by about 1.33 to know how much dry material to order. This calculator applies that factor plus your wastage percentage.
What mix ratio for wall plaster?
1:6 (one cement to six sand) for internal walls, 1:4 for external walls and ceilings, 1:5 as the middle ground for rough external work. Richer than 1:3 wastes cement and cracks more from shrinkage, leaner than 1:6 gets weak and powdery.