MistriCalc → Plaster Calculator
Plaster Calculator
Cement bags and sand for internal or external plaster — by area, coat thickness, and cement:sand mix, the way it is estimated on site.
Materials & quantities explainer
Run your numbers first, then read how it works. Start with the calculator below — the example values are pre-filled — then keep scrolling for the method, a worked example and the questions builders ask most. Everything runs in your browser; nothing you type is stored.
Calculator
To estimate plaster, multiply the area by the thickness for the wet volume, then by 1.27 for the dry volume, and split that by the cement:sand ratio. For 100 m² of 12 mm plaster in 1:6, you need about 6.27 bags of cement (≈ 314 kg) and 1.31 m³ of sand. A richer 1:4 mix for external walls uses more cement for the same area.
Key takeaways
- Wet volume = area × thickness.
- Dry volume = wet × 1.27.
- 12 mm internal, 15–20 mm external/rough.
- 1:6 internal, 1:4 external/wet areas.
- Add 10–20% for wastage and uneven surfaces.
How plaster quantities are calculated
Plaster is a thin layer of cement mortar. The tool finds the volume of that layer, bulks it to a dry volume, and divides by the mix to get cement and sand.
Convert sand to tonnes by × 1.55 (≈ 1,550 kg/m³) and to CFT by × 35.3147.
Worked example: plastering a 3 BHK's 200 m² of walls
Say you have 200 m² of internal walls at 12 mm, mix 1:6. Wet = 200 × 0.012 = 2.4 m³; dry = 2.4 × 1.27 = 3.048 m³. Cement = 3.048 ÷ 7 = 0.4354 m³ ÷ 0.0347 ≈ 12.55 bags (≈ 628 kg). Sand = 3.048 × 6/7 ≈ 2.61 m³ (≈ 4.05 tonne). With 15% wastage, order about 14.4 bags and 3.0 m³ of sand.
Cement per m² by thickness and mix
| Mix | Thickness | Cement (bags/m²) | Sand (m³/m²) | m² per bag |
|---|---|---|---|---|
| 1:4 | 12 mm | 0.0879 | 0.0122 | ≈ 11.4 |
| 1:6 | 12 mm | 0.0627 | 0.0131 | ≈ 15.9 |
| 1:4 | 15 mm | 0.1098 | 0.0152 | ≈ 9.1 |
| 1:6 | 15 mm | 0.0784 | 0.0163 | ≈ 12.8 |
| 1:4 | 20 mm | 0.1465 | 0.0203 | ≈ 6.8 |
| 1:6 | 20 mm | 0.1045 | 0.0218 | ≈ 9.6 |
Per-m² figures use the 1.27 dry factor and a 0.0347 m³ cement bag; add wastage on top.
Where this fits in your build
Plaster goes on after the masonry — size the wall first with the brick calculator, then paint it with the paint calculator. For RCC surfaces behind the plaster, the concrete calculator covers cement, sand and aggregate.
Frequently asked questions
How much cement and sand to plaster 100 m²?
At 12 mm, 1:6: wet 1.2 m³ → dry 1.524 m³ → ≈ 6.27 bags cement (≈ 314 kg) and ≈ 1.31 m³ sand.
Why multiply by 1.27?
Dry material bulks up and has voids that close on mixing, so the dry volume is about 1.27× the finished wet plaster.
What plaster thickness should I use?
12 mm internal, 15–20 mm external/rough, 6–10 mm ceilings. Thicker plaster needs proportionally more material.
1:4 vs 1:6?
1:4 is richer (external/wet areas), 1:6 is leaner (internal). The richer mix uses more cement per m².
How many bags for 1 m² of 12 mm plaster?
About 0.063 bags at 1:6 — roughly 16 m² per bag at this thickness and mix.
Should I add wastage?
Yes — 10–20% for wastage, uneven walls and keying coats. Round the cement bags up.
Plaster quantities follow standard cement-mortar practice and standard plastering codes, with the proportioning approach of nominal mortars. The 1.27 dry-volume factor, 50 kg / 0.0347 m³ cement bag and sand density ≈ 1,550 kg/m³ are standard trade values.
Last reviewed 2026-06-14