Wall plaster = (wall area − openings) × faces + reveals. A 12 × 3 m wall with one door and two windows, plastered both sides with 100 mm reveals, is 62.5 + 2.9 = 65.4 m². At 12 mm and 1:5 that is 4.8 bags of cement and 0.83 m³ of sand.
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Plaster area (faces + reveals)
65.4m²
Wall faces
62.5 m²
Reveals (jambs, heads, sills)
2.9 m²
Cement (50 kg bags)
4.8 bags (239 kg)
Sand
0.83 m³
Wet plaster
0.785 m³
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Reveals = (doors × (2H + W) + windows × 2(H + W)) × depth × 2 = 2.9 m²
Wet plaster = 65.4 m² × 12 mm = 0.785 m³ → × 1.27 dry → cement 4.78 bags
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Generated with myconstructioncalculator.com. Estimates for planning and ordering only; verify against drawings and specifications.
Formula
Faces = (L × H − openings) × number of facesReveals = (doors × (2H + W) + windows × 2(H + W)) × reveal depth × facesArea = faces + reveals
Worked Example
A 12 × 3 m wall, one 0.9 × 2.1 m door, two 1.2 × 1.2 m windows, both faces, 100 mm reveals, 12 mm 1:5:
Openings = 1.89 + 2.88 = 4.77 m² → faces = (36 − 4.77) × 2 = 62.5 m²
Reveals = (5.1 + 2 × 4.8) × 0.1 × 2 = 2.9 m²
Area = 65.4 m² → 0.785 m³ wet → 4.8 bags, 0.83 m³ sand
Reveal Area per Opening, One Face (100 mm deep)
Opening
Reveal area
Door 0.9 × 2.1 m (3 sides)
0.51 m²
Window 1.2 × 1.2 m (4 sides)
0.48 m²
Window 1.5 × 1.2 m
0.54 m²
Window 2.4 × 1.5 m
0.78 m²
Frequently Asked Questions
Do I add window and door reveals to plaster area?
Yes. The jambs, heads and sills inside each opening are plastered too. For a 1.2 × 1.2 m window with 100 mm reveals that is 0.48 m² per face.
How do I calculate plaster for both sides of a wall?
Work out the net area of one face (length × height − openings), multiply by two, and add the reveals on both faces.
How thick should wall plaster be?
Commonly 12 mm on brick or block walls, 15 mm where they are rough, and 6–10 mm on smooth concrete.
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