Roof Slab Casting, Concrete & Wall Plaster Calculator

Calculate exact 50kg cement bags, coarse sand in CFT, stone chips aggregate, and mixing water for M15, M20, M25 Concrete Casting and 12mm / 15mm Wall Plaster as per IS 456 standards.

Total Wet Volume (ভিজে আয়তন): 0 CFT
Cement Bags (৫০ কেজি বস্তা): 0 Bags
Coarse Sand (মোট বালি): 0 CFT
Stone Chips Aggregate (পাথর কুচি): 0 CFT
Estimated Mixing Water (জল): 0 Liters
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Indian Standard IS 456 Concrete & Plaster Mix Ratio Guidelines

Estimating raw building materials accurately before casting prevents site delays and controls procurement costs. In residential construction across India and West Bengal, M20 Grade (1:1.5:3) is the standard structural benchmark for roof slabs, beams, lintels, and foundation plinths. Before slab casting, verify structural steel requirements via our TMT Steel Rod Weight Calculator and masonry layouts with the Red Brick Counter.

IS 456 Concrete Mix Ratios and Dry Volume Mechanics M20 Nominal Concrete (1:1.5:3) 1 Cement 1.5 Sand 3 Stone Dry Factor = 1.54 multiplied by Wet Volume Wall Plaster Mortar (1:6 / 1:4) 1 Cement 4 to 6 Sand Dry Factor = 1.33 multiplied by Wet Volume
Figure 1.1: Nominal Mix Volumetric Proportions and Void Shrinkage Conversion (IS 456).

1. Nominal Concrete Mix Ratios & Material Yield Chart

Standard material proportions per 100 Sq. Ft. of 5-inch thick RCC slab casting (Dry Volume Factor = 1.54):

Concrete Grade Mix Proportion (C : S : A) Cement (50kg Bags) Sand (CFT) Stone Chips (CFT) Structural Application
M20 Grade1 : 1.5 : 3~9.6 Bags~17.5 CFT~35.0 CFTRoof Slabs, Beams, Lintels (Standard)
M25 Grade1 : 1 : 2~13.2 Bags~16.0 CFT~32.0 CFTHeavy Columns & Multi-Storey Foundations
M15 Grade1 : 2 : 4~7.5 Bags~18.5 CFT~37.0 CFTPlain Cement Concrete (PCC Floor Base)
12mm Plaster1 : 6 (Mortar)~1.8 Bags~13.5 CFTNilInterior Brick Wall Finishing
15mm Plaster1 : 4 (Mortar)~3.2 Bags~16.0 CFTNilExterior Weather-Proof Wall Plaster

2. The Science of Dry Volume Conversion (1.54 & 1.33 Factors)

When cement, sand, and stone chips are mixed with water, the fine cement particles fill the air voids between sand and aggregate grains. Consequently, the wet volume shrinks by roughly 33% to 35% compared to the dry volume:

  • Concrete Dry Volume: Dry Volume equals Wet Volume in CFT multiplied by 1.54.
  • Plaster Mortar Dry Volume: Dry Volume equals Wet Volume in CFT multiplied by 1.33, plus a 20 percent joint-filling and wastage buffer.
  • 1 Cement Bag Volume: 50 kg equals 1.226 CFT (0.0347 cubic meters).

Planning wall finishes next? Estimate room paint and primer quantities with the Wall Paint & Putty Estimator and calculate room floor tiles through our Floor Tiles & Marble Box Tool.

Frequently Asked Questions (FAQ)

Answers to common questions regarding roof casting, plaster ratios, and cement estimations.

For a 1000 sq. ft. roof slab with a 5-inch thickness using standard M20 grade concrete (1:1.5:3 ratio), you will need approximately 95 to 98 bags of cement (50 kg each), 175 CFT coarse sand, and 350 CFT stone chips (aggregate).
Interior brick walls typically use a 12mm thickness with a 1:6 cement-sand ratio. Exterior walls exposed to rain require a 15mm to 20mm thickness with a richer 1:4 mix and waterproofing liquid.
As per IS 456 water-cement ratio guidelines (0.45 to 0.50), approximately 25 to 28 liters of clean water is required per 50 kg bag of cement for optimal strength and workability.

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