---
title: "Materials for 12 cm RCC slab"
subject: "Estimating and Costing"
chapter: 4
key: "semester_7/estimating_and_costing:materials-rcc-slab-12cm"
source: https://www.bctengineer.com/q/semester_7/estimating_and_costing/materials-rcc-slab-12cm
site: BCT Engineering
---

# Materials for 12 cm RCC slab

Estimating and Costing · Chapter 4: Analysis of Rates

- Asked in: 2073 Shrawan, 4 marks
- Video: [RCC Slab Estimation | Materials Quantity Calculation](https://www.youtube.com/watch?v=3oJo1dzvbH0) — Learn Civil Tech & Tricks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/estimating_and_costing/materials-rcc-slab-12cm
- Whole chapter: https://www.bctengineer.com/md/semester_7/estimating_and_costing/chapter-4

## Question

Estimate the quantities of cement, sand and coarse aggregate required for 12 cm thick RCC slab of (1:1½:3) mix proportion. The outside dimensions of slab are 4.20 m × 3 m.

## Short answer

Slab volume is 1.512 m³; dry volume 2.328 m³ for 1:1.5:3 mix. Cement = 12.2 bags (0.423 m³), sand = 0.635 m³, coarse aggregate = 1.270 m³.

## Answer

Assumptions: dry volume = 1.54 × wet volume for concrete and 1.27 × wet volume for mortar; 1 m³ of cement = 28.8 bags of 50 kg; no wastage is added. The slab is taken as one rectangle of the outside dimensions given and the volume of steel is not deducted.

- Volume of slab $= 4.20 \times 3.00 \times 0.12 = 1.512$ m³

**Concrete 1:1½:3**
- Wet volume $= 1.512$ m³; dry volume $= 1.54 \times 1.512 = 2.328$ m³ (sum of ratio $= 5.5$)
- Cement $= 1/5.5 \times 2.328 = 0.423$ m³ $= 0.423 \times 28.8 = 12.2$ bags (50 kg)
- Sand $= 1.5/5.5 \times 2.328 = 0.635$ m³
- Coarse aggregate $= 3/5.5 \times 2.328 = 1.270$ m³

**Answer: cement = 12.2 bags (0.423 m³); sand = 0.635 m³; coarse aggregate = 1.270 m³.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Slab volume?
   A. 4.2 x 3 = 12.6
   B. 1.512 x 1.54
   C. 4.20 x 3.00 x 0.12 = 1.512 m^3
   D. 0.12 x 3 x 3
   Answer: C. Length x width x thickness. (Key point: Volume)

2. Is steel deducted?
   A. Yes 0.8%
   B. No, volume not deducted
   C. Yes 2%
   D. Yes, doubled
   Answer: B. Stated assumption. (Key point: Steel)

3. Cement?
   A. 1/5.5 x 2.328 = 0.423 m^3 = 12.2 bags
   B. 1/5.5 x 1.512
   C. 1/3 x 2.328
   D. 1/4.5 x 2.328
   Answer: A. Dry = 1.54 x 1.512. (Key point: Cement)

4. Sand, aggregate?
   A. 1.270 and 0.635
   B. 0.423 and 0.846
   C. 1.0 and 2.0
   D. 0.635 m^3 and 1.270 m^3
   Answer: D. 1.5/5.5 and 3/5.5 of dry. (Key point: Sand and aggregate)

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