Cement is the binding agent in concrete and mortar — a fine grey powder that, when mixed with water, undergoes a chemical reaction called hydration and hardens, gluing sand and aggregate into a solid mass. It is the most expensive of the basic concrete ingredients, so getting the cement quantity right matters both structurally and financially.
The most common types in Indian house construction are Ordinary Portland Cement (OPC, in grades 33, 43 and 53) and blended cements such as Portland Pozzolana Cement (PPC) and Portland Slag Cement (PSC), which incorporate fly ash or slag for durability and lower cost. Cement is sold in standard 50 kg bags; one bag occupies about 0.0347 m³ (1.226 cft), based on a bulk density of roughly 1440 kg/m³.
Estimating cement starts from the dry volume of concrete and the mix ratio, then converts the cement fraction into bags — usually with a small wastage allowance for spillage on site.