you can do this rather easy
On your serial interface it shoes 5 minute input/output rate see below
GigabitEthernet0/3 is up, line protocol is up
Hardware is BCM1250 Internal MAC, address is 0005.9ae9.f019 (bia 0005.9ae9.f019)
MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, link type is force-up, media type is LX
output flow-control is XON, input flow-control is XON
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/42/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 10556000 bits/sec, 1678 packets/sec
5 minute output rate 13685000 bits/sec, 4366 packets/sec
897675130 packets input, 4235279523 bytes, 0 no buffer
Received 0 broadcasts, 2 runts, 0 giants, 0 throttles
0 input errors, 2 CRC, 0 frame, 72 overrun, 0 ignored
0 watchdog, 83855 multicast, 0 pause input
2 input packets with dribble condition detected
1356347449 packets output, 1424650700 bytes, 0 underruns
0 output errors, 0 collisions, 5 interface resets
0 babbles, 0 late collision, 0 deferred
5 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
This is what you want to look at , however , this is just an average over 5 minutes , you can change this value to something lower
router#conf t
router#(conf)int s0/0
router#(conf-if)load-interval 30
this will calcualte the load over a 30 second period
by using the 'sh int s0/0 command'
