Hi,
If you do a show interface like this :
Mos-Eisley>show interface fastEthernet 1/0/1
FastEthernet1/0/1 is administratively down, line protocol is down (disabled)
Hardware is Fast Ethernet, address is 0015.c627.a003 (bia 0015.c627.a003)
Description: **** Untrusted Port To Remain Closed ****
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
The figures shown in red are percentage utilisation, so basically 128/255 would be 50% utilised. Also you can see packets per sec etc. These statistics are averaged over 5 minutes but can be changed per interface with the load-interval command (available from IOS 12.4 onwards). Load intervals can only be set between 30 and 600 seconds in 30 second increments.
HTH
Thanks
Steve