Plaster calculator
Example: 100 m² of 12 mm plaster in 1:6 → 1.2 m³ wet, 1.44 m³ with 20% extra, 1.83 m³ dry → about 7.5 bags (376 kg) of cement and 1.57 m³ of sand.
How much cement for plastering?
For 100 m² of 12 mm plaster in 1:6, you need about 7.5 bags of cement and 1.57 m³ of sand. Work it out as area × thickness, plus about 20% for filling joints and uneven surfaces, times a dry volume factor of 1.27, then split by the mix ratio. Thicker plaster or a richer mix needs proportionally more cement.
The formula
Add 20% for joints and uneven surface
Dry volume = × 1.27 (some use 1.33)
Cement (m³) = dry ÷ (1 + sand parts) · kg = m³ × 1,440 · bags = kg ÷ 50
Sand (m³) = dry × sand parts ÷ (1 + sand parts)
| Per 100 m² | 12 mm, 1:6 | 12 mm, 1:4 | 15 mm, 1:6 | 20 mm, 1:6 |
|---|---|---|---|---|
| Cement (bags) | 7.5 | 10.5 | 9.4 | 12.5 |
| Sand (m³) | 1.57 | 1.46 | 1.96 | 2.61 |
With 20% extra and a 1.27 dry factor, no extra wastage. Using 1.33 adds about 5%.
Thickness and mix: what's usual
- Internal walls: about 12 mm in a single coat. IS 1661, as commonly quoted, takes 12 mm for a single coat and two coats for thicker work.
- External walls: about 15–20 mm, usually in two coats.
- Ceilings: about 6 mm.
- Mix: 1:6 is common for internal walls; richer mixes such as 1:4 are used for external work and ceilings. Follow your specification, not a blog.
- Curing: at least 7 days.
Why published plaster figures are so far apart
Sites quote anything from about 0.066 to 0.092 bags per m² for 12 mm, 1:6 plaster, depending on whether they add the 20% allowance and wastage. A few figures in circulation are two to four times what the arithmetic supports. Before you order on the basis of any number, including ours, check how it was worked out. Every step is shown above.
Plaster on site: measure, bill, reconcile
Plaster is measured in m² in the measurement book (for example, "Plaster 12 mm CM 1:4") and billed through the abstract and RA bill. Comparing cement issued with the theoretical quantity catches waste early. See the measurement sheet, RA bill format and material reconciliation.
Frequently asked questions
How much cement is needed for 100 m² of 12 mm plaster?
About 7.5 bags (376 kg) in a 1:6 mix and about 10.5 bags in 1:4, allowing 20% extra for joints and uneven surfaces and a 1.27 dry factor.
What is the standard plaster thickness?
About 12 mm for internal walls, 15–20 mm for external walls in two coats, and about 6 mm for ceilings.
Which mix is used for plastering?
1:6 is common for internal walls, with richer mixes such as 1:4 for external work and ceilings. Follow your project specification.
Why multiply by 1.27 for plaster?
Dry cement and sand reduce in volume when mixed with water and voids fill, so you need more dry material than the wet volume. 1.27 is a common factor; 1.33 is also used.
How do I calculate plaster in sq ft?
Convert to m² (1 sq ft = 0.0929 m²), or select sq ft in the calculator. 1,000 sq ft is about 92.9 m².
How long should plaster be cured?
At least 7 days, keeping the surface moist.
Plaster me kitna cement lagta hai?
100 m² ke 12 mm plaster (1:6) me lagbhag 7.5 bag cement aur 1.57 m³ ret lagti hai. 1:4 mix me lagbhag 10.5 bag.
From plaster quantity to RA bill
Measure plaster in the app, bill it, and reconcile the cement, even on sites with no signal.
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