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PLASTER & MORTAR · PLASTERING CALCULATOR

Dry Volume of Plaster

Dry volume of plaster = area × thickness × a dry factor of about 1.27. 100 m² of 12 mm plaster is 1.2 m³ wet and 1.524 m³ dry; in a 1:4 mix that needs 8.78 bags of 50 kg cement and 1.22 m³ of sand.

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Surface
m²
mm
Mix
Plaster 1:4 on 100 m²Plaster 1:4 on 100 m²wall plaster 12 mmmyconstructioncalculator.comNot to scale
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Results

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Cement (50 kg bags)
8.78bags
Sand1.22 m³
Wet plaster volume1.200 m³
Cement weight438.9 kg
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Working
  1. Wet volume = area × thickness = 100.0 m² × 0.0120 m = 1.2000 m³
  2. Dry volume = 1.2000 × 1.27 = 1.5240 m³
  3. Cement = 1.5240 × 1 ÷ 5 = 0.3048 m³ = 8.78 bags
  4. Sand = 1.5240 × 4 ÷ 5 = 1.2192 m³
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formula


Wet volume = plaster area × thickness
Dry volume = wet volume × 1.27   (1.30 to 1.35 also used)
Cement     = dry volume ÷ (1 + sand parts)       → × 1,440 kg/m³ ÷ 50 kg = bags
Sand       = dry volume × sand parts ÷ (1 + sand parts)


Worked Example


100 m² of 12 mm plaster in 1:4:


    

  1. Wet volume = 100 × 0.012 = 1.2 m³
    2. 

  2. Dry volume = 1.2 × 1.27 = 1.524 m³
    3. 

  3. Cement = 1.524 ÷ 5 = 0.305 m³ × 1,440 = 438.9 kg = 8.78 bags
    4. 

  4. Sand = 1.524 × 4 ÷ 5 = 1.22 m³
    5. 



Cement and Sand per 100 m² of Plaster


Dry factor 1.27, 50 kg bags.






Thickness
Mix
Cement
Sand






12 mm
1:4
8.78 bags
1.22 m³




12 mm
1:6
6.27 bags
1.31 m³




15 mm
1:4
10.97 bags
1.52 m³




15 mm
1:6
7.84 bags
1.63 m³




20 mm
1:4
14.63 bags
2.03 m³




20 mm
1:6
10.45 bags
2.18 m³






More Dry Volumes
Frequently Asked Questions
Why is the plaster dry factor 1.27 and not 1.33?
Both are used. 1.27 allows for voids and bulking of sand; many estimators add a little more, using 1.30 to 1.35, to cover uneven walls and joints. Change the factor in the calculator to match your site.
How much cement is needed for 100 m² of 12 mm plaster?
In 1:4 mix, about 8.78 bags of 50 kg: 100 × 0.012 = 1.2 m³ wet, × 1.27 = 1.524 m³ dry, ÷ 5 = 0.305 m³ of cement × 1,440 kg/m³ = 439 kg. In 1:6 mix it is about 6.27 bags.
What thickness of plaster should I use?
Typical figures are 12 mm for internal walls, 15 to 20 mm for external walls in two coats, and 6 mm for ceilings. Follow your specification.