Out of order arrival of packets is an inevitable phenomenon on the Internet. Application performance can degrade to a great extent due to out-of-order arrival of packets. Metrics to characterize the degree of re-ordering will promote the evaluation of network protocols with respect to packet reordering as well as provide a uniformly defined quantitative measure for packet reordering. We define the concept of "reorder density function" (RD), which quantitatively measures the degree of reordering in sequences of packets. While the reorder density function can provide a comprehensive picture on reordering, measures such as mean and median of reorder density can be used when simpler metrics are desired. Results of reordering analysis using the above metrics for TCP and UDP based applications under different network conditions are presented.