Hello Abhishek,
two possible approaches here:
worst case analysys: considering packets of smallest size
a sort of average analysis: considering packets of average size, let's say 500 bytes.
given a packet forwarding capabilities in pps you can find the equivalent bandwidth:
by dividing by 2 to take in account bidirectionality and then you multiply using the packet size
(pps/2) * packet_size* (1/8)
bits/byte
be aware that the only safe approach is the worst case analysys because performance data are given without any feature applied (ACLs, QoS, NAT) that reduce performance in software based routers.
Hope to help
Giuseppe