Plastering Calculation: Cement and Sand Per Square Metre
Plaster is one of the most repeated activities on any site, so a small error per square metre multiplies fast across a whole building. Here's the clean method.
The formula
- Area × thickness = wet volume. For 100 m² at 12 mm: 100 × 0.012 = 1.2 m³.
- Add for dry volume: wet × 1.27 = 1.52 m³ (mortar shrinks when mixed).
- Split by ratio. For 1:6, total parts = 7.
Worked example (1:6, 100 m²)
- Cement = 1.52 × (1/7) ÷ 0.0347 ≈ 6.2 bags
- Sand = 1.52 × (6/7) ≈ 1.3 m³
Scale it down for smaller areas — for 100 sq ft (≈9.3 m²) that's roughly 0.9 bag cement + 6 cft sand.
Ratios by surface
| Surface | Ratio | Thickness |
|---|---|---|
| Internal wall | 1:6 | 12 mm |
| External wall | 1:4 | 15–20 mm |
| Ceiling | 1:3 | 6 mm |
Control the wastage
Plaster wastage hides in over-mixing and dropped mortar. When each bag is logged against the project, planned-vs-actual becomes obvious. Vystra's material tracking keeps cement and sand quantities tied to each site, so overspend shows up while you can still fix it.
Frequently asked questions
How much cement is needed for plastering 100 sq ft?
For 12 mm internal plaster (1:6 ratio), 100 sq ft needs roughly 0.9–1.0 bag of cement and about 6 cft of sand.
What is the cement-sand ratio for plastering?
Common ratios are 1:6 for internal walls, 1:4 for external walls and 1:3 for ceilings. Thicker or exposed surfaces use richer mixes.
What is the standard plaster thickness?
Internal plaster is usually 12 mm, external plaster 15–20 mm, and ceiling plaster 6 mm.
Track projects, workers, materials & payments
Vystra is construction-management software made for Indian civil contractors — projects, attendance, wages, materials, P/L and GST quotations with built-in calculators.
Start free →