The disclosure relates to method and system for determining network congestion level. The method includes determining a round trip time (RTT) for each high priority and for each low priority packet transaction in the precision time protocol (PTP) protocol. The high priority and the low priority packet transactions are conducted between a master device and a slave device within a pre-defined time window. The method further includes determining an average high priority RTT and an average low priority RTT based on the RTT for each high priority packet transaction and for each low priority packet transaction respectively, computing an average delta RTT based on a difference between the average high priority RTT and the average low priority RTT, and determining an instantaneous network congestion level based on the average delta RTT and a reference delta RTT for a number of pre-defined time windows since a start of the slave device.