The view of pair sum labeling has been introduced in this work. Pair sums labeling behavior of complete graph, cycle, path, bistar etc. Here we study pair sum labeling of union of some standard graphs and we find the maximum size of a pair sum graph. Although its primary interest was the graceful labeling of trees in order to solve Ringel’s conjecture, labeling of graphs gained over the years its own beauty and interest. All the graphs considered here are finite and undirected. The graph labeling is an assignment of integers to the vertices or edges or both subject to certain conditions. If the domain of the mapping is the set of edges then the labelling called pair sums a labeling.