Network Interface utilization on centos 7 doesnt show correct value


I am trying to capture utilization of network interface in percentage with respect to its speed.
In my lab, i have centos 7 with 1000Mb/s interface speed. I used below mathematical expression to achieve it, however I get graph with utilization reaches to ~200% when run iperf. I am not quite sure how is that possible with 1000Mb/s speed on interface.
To get percentage:
100 *(sum(rate(node_network_receive_bytes_total{device=“ens33”}[1m])) by (device, instance) * on(instance) group_left(nodename) (node_uname_info) + sum(rate(node_network_transmit_bytes_total{device=“ens33”}[1m])) by (device, instance) * on(instance) group_left(nodename) (node_uname_info)) / on(instance) node_network_speed_bytes{device=“ens33”}

To get Network Traffic stats:
irate(node_network_receive_bytes_total{instance=“”,device=“ens33”}[1m]) * 8

irate(node_network_transmit_bytes_total{instance=“”,device=“ens33”}[1m]) * 8

Please suggest, if there is any missing or whats best way to approach the network percentage utilization of network interface in linux.