01 Dec 2025

Introduction

Plastering is an essential part of building construction. It creates a smooth, durable surface on walls and ceilings, protects the structure from moisture, and prepares the surface for painting.

To achieve a consistent and high-quality finish, it is important to estimate cement quantity accurately. Overestimation increases cost, while underestimation can affect work quality and project timelines.

This guide will help you calculate the exact amount of cement needed for plastering, using a simple and accurate method.

Standard Assumptions Used for Calculation

  • Wall area: 100 m²
  • Thickness: 12 mm (0.012 m)
  • Mix ratio: 1:6 (Cement:Sand)
  • Dry volume factor = 1.33
  • Cement density: 1440 kg/m³
  • Cement bag = 50 kg

These values are commonly used in Nepal for residential and commercial plastering.

Step-by-Step Calculation

1.  Calculate Wet Volume of Plaster

  Wet Volume:

                         =Area × Thickness 

                         = 100 × 0.012 = 1.2 m³

2. Convert Wet Volume to Dry Volume

 Dry Volume:

                          = Wet Volume * 1.33

                          =1.2 × 1.33 

                          = 1.596 m³

3. Calculate Cement Quantity

Since the mix ratio is 1:6, total parts = 1+6 =7 parts.

Cement Volume: 

                            = (1/7) * Dry Volume

                            = (1/7) * 1.596

                            = 0.228 m³

4. Convert Cement Volume to Weight

Weight: 

                             = Volume * Density

                             = 0.228 * 1440 

                             = 328.32 Kg

5. Convert Cement Weight to Bags

Number of Bags:

                              = 328.32 ÷ 50

                              = 6.57 bags

Final Answer: How Many Cement Bags Are Needed?

You need approximately 7 cement bags for 100 m² of plastering at 12mm thickness with a 1:6 mix.

Pro Tips for Better Plastering Results

1. For External Walls

Use Sarbottam OPC 43 Cement 

  •  Provides higher early strength
  • Offers better bonding and crack resistance
  • Suitable for exterior durability

Learn More: What is Ordinary Portland Cement?

2. For Internal Walls

Use Sarbottam PPC Cement

  • Better Workability
  • Smoother finish
  • Lower heat of hydration
  • Ideal for aesthetic interior plaster

Learn More: What is Pozzolana Portland Cement(PPC)?

3. For Bathrooms, Kitchens & Wet Areas

Use waterproofing additives or polymer-based bonding agents for improved moisture resistance. 

Conclusion

Accurate cement calculation ensures material savings, higher efficiency, and consistent plaster quality. Whether you are a homeowner or a site engineer, using the right cement in the right quantity is key to a durable, long-lasting finish.

For best results, choose Sarbottam OPC and PPC, manufactured with advanced VRM technology and certified under NS 572, ensuring strength, consistency, and superior performance for every project.

FAQs for “Cement Calculation for Plastering”

1. How much cement is required for plastering per square meter?

For 12 mm thick plaster using a 1:6 cement–sand ratio, cement consumption is approximately 0.07 bags per m² (about 3.3–3.5 kg per m²).

2. How many cement bags are needed for 100 m² plastering?

You need approximately 7 bags of cement to plaster 100 m² of wall area at 12 mm thickness using a 1:6 mix ratio.

3. What is the standard plaster thickness for walls?

The standard plaster thickness is:

Internal walls: 10–12 mm

External walls: 12–15 mm

Thicker plaster increases cement consumption.

4. Which cement–sand ratio is best for plastering?

The most commonly used plastering mix is 1:6 (cement:sand) for both internal and external walls.

For areas exposed to moisture, a 1:4 or 1:5 mix may be used for higher strength.

5. Does plaster thickness affect cement quantity?

Yes. Cement consumption increases directly with plaster thickness.

For example:

10 mm plaster → less cement

15 mm plaster → significantly more cement

Always measure thickness accurately before estimation.