In the world of construction, accuracy and precision are not luxuries—they are necessities. From the foundation of a small home to the towering columns of a skyscraper, the integrity of every structure depends on correct proportions of materials. Among these, sand is one of the most widely used fine aggregates in concrete, mortar, and plaster. But there’s a phenomenon that often confuses even experienced site engineers and can lead to costly mistakes if overlooked: the bulking of sand. Bulking of sand refers to the increase in the volume of sand due to moisture. This deceptively simple concept has far-reaching implications for construction quality, cost efficiency, and safety. To truly understand why bulking occurs and how to account for it, we need to explore its science, practical impacts, and the best practices used on construction sites worldwide.