Although empirical method is easy to use in determining the materials requirement for Nominal Concrete mix, it sometimes doesn’t give accurate results as it doesn’t take into factor the local variations in the materials.

Let’s design C20 grade concrete. Ratio for C20 concrete is 1 : 2 : 4

Step-1: Calculate the Volumes of material required in 1 Cum concrete

The dry volume of concrete mixture is always greater than the wet volume. The ratio of dry volume to the wet volume of concrete is 1.54.

So 1.54 Cum of dry materials (cement, sand and aggregate) is required to produce 1 Cum of concrete

Volume of Cement required = 1/(1+2+4) X 1.54 = 1/7 X 1.54 = 0.22 Cum

Volume of Sand required = 2/7 X 1.54 = 0.44 Cum or 15.53 cft

Volume of Aggregate required = 4/7 X 1.54 = 0.88 Cum or 31.05 cft

Note: 1 cubic meter = 35.29 cubic feet


Step-2: Calculate the weights of materials required in 1 Cum concrete

Density of Cement (loose) = 1440 kg/cum

So weight of cement required = 1440 X 0.22 = 316.2 Kgs or 6.32 bags

Density of Sand = 1600 Kgs/cum

Weight of Sand required = 1600 X 0.44 = 704 kgs

Density of Aggregate = 1450 kgs/cum

Weight of aggregate required = 1450 X 0.88 = 1,276 Kgs