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Plaster Calculator: Cement and Sand for 12, 15 and 20 mm Plaster

Enter the total wall length and height to plaster, deduct openings, and pick thickness and mix. You get the plaster area, cement bags and sand.

Cement (50 kg bags)

3bags

Plaster area
30 m² · 322.9 sq ft
Cement weight
113 kg
Sand
0.47 m³ · 16.6 cft
Plaster (wet)
0.36 m³ · 12.7 cft

Estimate only, based on standard thumb rules. Confirm quantities with your engineer or contractor before you buy.

Show working
  1. A = 10 × 3 = 30 m²
  2. V = 30 × 0.012 = 0.36 m³
  3. V dry = 0.36 × 1.2 × 1.27 = 0.549 m³
  4. Cement = 0.549 × 1/7 × 1440 = 112.9 kg ÷ 50 = 2.26 → 3

How to use

  1. Enter the total length of walls and their height.
  2. Deduct door and window area, pick 12, 15 or 20 mm thickness.
  3. Choose the mix ratio to see cement and sand.

Good to know

Wet volume = area × thickness. Brick walls are uneven, so 20% is added for filling joints and hollows, then × 1.27 for dry volume (a common Indian estimating rule). Both numbers can be changed under More options.

Typical choices: 12 mm in 1:6 for inside brick walls, 15 mm on rough faces, 20 mm in 1:4 (often in two coats) for outside walls, and 6 mm in 1:3 or 1:4 for ceilings. Count both faces of a wall if you plaster both.

Per 100 m² of 12 mm, 1:6 plaster this method gives about 7.5 bags of cement and 1.6 m³ of sand. Smooth block walls need less; very rough or out-of-plumb walls need more. Cure plaster with water for at least 7 days.

Questions

How much cement for 100 sq ft of 12 mm plaster?

100 sq ft = 9.29 m² → wet 0.111 m³ → +20% and × 1.27 = 0.17 m³ dry. In 1:6, cement is 1/7 = 0.024 m³ × 1440 = 35 kg, about 0.7 bag.

Which thickness should I use?

Inside walls usually 12 mm, uneven walls 15 mm, outside walls 20 mm. Ceilings 6 mm.

Why add 20%?

Brick faces have joints and dips that fill with mortar, and some mortar falls. 20% is a common allowance; use less on smooth block walls.

1:4 or 1:6?

1:4 is richer and used outside or in wet areas; 1:6 is common for inside walls.

Do I count both sides of a wall?

Yes, if both sides are plastered. Enter the total length of all faces.

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