12 pairs (24). 8-12 rib pairs are called false ribs.
Our thoracic cage or rib cage is composed of 12 pairs of ribs, sternum, cartilages and thoracic vertebrae. Of the 12 pairs of ribs, the first 7 pairs (1-7) are attached to vertebrae posteriorly and sternum anteriorly (with costal cartilage). These rib pairs are called true ribs.
8-12 rib pairs are attached to vertebrae posteriorly, but anteriorly they are not attached to the sternum directly.These rib pairs are called False ribs. The 8-10 rib pairs connect to the sternum indirectly via the costal cartilages of the ribs above them. The 11 and 12 rib pairs do not connect to the sternum at all. So, these two rib pairs have another name, the floating ribs .