Step-by-Step Guide To Calculating Concrete Material Quantities For A Slab

Estimating concrete materials accurately is essential for cost-effective slab construction. Here’s a detailed breakdown based on a real-world slab example to help you understand how to compute the required quantities of cement, sand, and granite.

Slab Dimensions and Volume Calculation

The slab in question includes a main rectangular section and a smaller extended part.

Main slab dimensions:

• Length = 32 meters

• Width = 18 meters

• Thickness = 0.15 meters

Extension dimensions:

• Length = 5 meters

• Width = 3.6 meters

• Thickness = 0.15 meters

Total Volume of Slab (Wet Volume):

Wet Volume = (32×18×0.15) + (5×3.6×0.15) = 89.1m³

Converting Wet Volume to Dry Volume

Concrete mix shrinks after placement. To account for this, multiply by a factor of 1.54:

Dry volume = 1.54 × 89.1 = 137m³

Concrete Mix Ratio Used

The standard mix ratio applied here is:
1: 1.5 : 3 (Cement: Sand: Aggregate)

Total mix proportion = 1 + 1.5 + 3 = 5.5

Cement Quantity Calculation

Cement portion = 1/(1+1.5+3) = 1/5.5 of the total mix

Cement volume = (1/5.5) × 137 = 24.9m³

Convert Volume to Weight: Cement density = 1440 kg/m³

Convert to weight: 24.9 × 1440 = 35,856kg

Convert to Bags: 1 bag = 50 kg

Convert to bags: 35,856 ÷ 50 = 717 bags

Sand Quantity Calculation

Sand portion = 1.5/5.5 of the total mix

Sand volume = (1.5/5.5) × 137 = 37.4m³

Aggregate Quantity Calculation

Aggregate portion = 3/5.5 of the total mix

Aggregate volume = (3/5.5) × 137 = 74.7m³

Summary of Quantities Required