Plaster Quantity Calculation: Cement and Sand per 100 m²

For 100 m² of 12 mm thick cement plaster in 1:6 you need about 7.5 bags of cement (376 kg) and 1.57 m³ of sand (about 55 cft). For 20 mm plaster, a 1:4 mix needs about 17.6 bags of cement and 2.44 m³ of sand, and a 1:6 mix needs about 12.5 bags and 2.61 m³ of sand.

These figures include 20% extra for uneven surfaces, joint filling and wastage, plus a wet-to-dry factor of 1.27. Below is the method, so you can repeat it for any area, thickness or mix.

The method in four steps

1. Wet volume = plastered area × thickness. For example, 100 m² × 0.012 m = 1.2 m³.
2. Add for uneven surfaces and wastage. Brick walls are never perfectly true, and the mortar also fills the raked joints. Add 20% for this.
3. Convert to dry volume. Dry cement and sand contain voids that disappear when you add water, so multiply by 1.27.
4. Split by the mix ratio. For 1:6, cement is 1/7 and sand is 6/7 of the dry volume. Cement weighs 1440 kg/m³, so one 50 kg bag is 0.0347 m³. One m³ is 35.31 cft.

Which thickness and mix is used where

Common Indian practice is listed below, but always follow the project specification.

• 12 mm, 1:6 on internal walls on the fair (smooth) side of brickwork
• 15 mm, 1:6 on the rough side of a wall
• 20 mm, 1:4 or 1:6 on external walls, often in two coats
• 6 mm, 1:3 on RCC ceilings

12 mm plaster in 1:6: per 100 m²

1. Wet volume = 100 × 0.012 = 1.20 m³
2. Add 20%: 1.20 × 1.20 = 1.44 m³
3. Dry volume = 1.44 × 1.27 = 1.829 m³
4. Cement = 1.829 ÷ 7 = 0.2613 m³ × 1440 = 376 kg = 7.5 bags
5. Sand = 1.829 × 6/7 = 1.568 m³ ≈ 55.4 cft

20 mm plaster in 1:4 and 1:6: per 100 m²

1. Wet volume = 100 × 0.020 = 2.00 m³
2. Add 20%: 2.00 × 1.20 = 2.40 m³
3. Dry volume = 2.40 × 1.27 = 3.048 m³
4. 1:4 (5 parts): cement = 3.048 ÷ 5 = 0.6096 m³ = 878 kg = 17.6 bags, and sand = 3.048 × 4/5 = 2.438 m³ ≈ 86 cft
5. 1:6 (7 parts): cement = 3.048 ÷ 7 = 0.4354 m³ = 627 kg = 12.5 bags, and sand = 3.048 × 6/7 = 2.613 m³ ≈ 92 cft

Quick reference table

All quantities except cement kg per m² are per 100 m² of plaster, with 20% added for surface and wastage and a dry factor of 1.27.

Worked example: plastering one room

The room is 4.0 m × 3.5 m on plan with 3.0 m clear height. It has one door (1.0 × 2.1 m) and two windows (1.2 × 1.2 m each). The walls get 12 mm plaster in 1:6 and the ceiling gets 6 mm plaster in 1:3.

Walls

1. Gross wall area = perimeter × height = 2 × (4.0 + 3.5) × 3.0 = 45.0 m²
2. Openings = door 2.10 + windows 2 × 1.44 = 4.98 m²
3. Net area = 45.0 − 4.98 = 40.02 m²
4. Wet volume = 40.02 × 0.012 = 0.480 m³
5. Add 20%: 0.480 × 1.20 = 0.576 m³
6. Dry volume = 0.576 × 1.27 = 0.732 m³
7. Cement = 0.732 ÷ 7 = 0.1046 m³ × 1440 = 151 kg ≈ 3.0 bags
8. Sand = 0.732 × 6/7 = 0.627 m³ ≈ 22.2 cft

Ceiling

1. Area = 4.0 × 3.5 = 14.0 m², so the wet volume = 14.0 × 0.006 = 0.084 m³
2. Adding 20% gives 0.1008 m³, and multiplying by 1.27 gives a dry volume of 0.128 m³
3. Cement = 0.128 ÷ 4 = 0.032 m³ = 46 kg ≈ 0.9 bag
4. Sand = 0.128 × 3/4 = 0.096 m³ ≈ 3.4 cft

Total for the room: about 197 kg of cement (3.9 bags, so buy 4) and 0.72 m³ of sand (about 25.5 cft).

To get plaster, brickwork and concrete quantities for a whole house together, use the Nirmaan house estimator.

Site tips and common mistakes

• Ordering on wet volume. Using area × thickness alone under-orders by about a third.
• Ignoring bulking of sand. Damp sand measured by volume bulks noticeably, often by 15–30% depending on moisture. Batch with dry sand or correct for bulking, or the plaster ends up lean.
• Using a thick coat to hide bad brickwork. Every extra 5 mm adds about 40% to a 12 mm plaster's material. Check the wall for plumb before you start plastering.
• Skipping preparation. Rake the joints, hack smooth concrete surfaces and wet the wall before plastering. Fix level dots and screeds so the thickness stays even.
• Poor curing. Keep the plaster moist for at least 7 days, as is common practice. See curing of concrete. PPC suits plaster work well, as explained in OPC vs PPC vs PSC.