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Plaster Calculator

Plaster weight is estimated by multiplying wall area by thickness and a density factor (about 1.6 kg per m² per mm). This gives a quick kilogram estimate for buying plaster bags or mixing on site.

What Is Plaster?

Plaster weight is the mass of plaster needed to cover a wall surface, calculated as area multiplied by thickness and a density factor of about 1.6 kg per m² per mm. This factor approximates the wet plaster density. Plaster is sold in bags, usually 25 kg or 40 kg.

Formula: Area x Thickness x 1.6

Example

Formula: Area x Thickness x 1.6 kg/m²/mm
= 30 m² x 12 mm x 1.6 kg/m²/mm
= 576 kg

Select area and thickness units, then the result will be in kg.

Tip: Choose your result unit on the right before calculating.

Step-by-step calculation

  1. Enter wall area and thickness with units.
  2. Calculate to see plaster weight in kg.

How this is calculated

Plaster volume = wall or ceiling area times plaster thickness (typically 12–15 mm for internal work). Mass = volume times plaster density (about 1200 kg/m³ for gypsum-based), plus 5–10% wastage.

Sources: IS 1543 (Code of practice for plastering); ASTM C926 (Sprayed Gypsum Plaster).

FAQ

How do I calculate plaster by hand?
Multiply area (m²) by thickness (mm) by 1.6. Example: 30 m² x 12 mm x 1.6 = 576 kg.
What is the formula for plaster weight?
Weight = Area x Thickness x 1.6 kg/m²/mm. The 1.6 factor approximates plaster density.
Plaster vs skim coat
Plaster is the base coat; skim coat is a thin finish layer. Both use similar weight formulas.
What units should I use?
Use m² or cm² for area, mm or cm for thickness, and kg for result.
Can I use this for external walls?
Yes. Enter external wall area and thickness. Add extra for rough surfaces.

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