#sh int s0/0.1
MTU 1500 bytes, BW 512 Kbit, DLY 20000 usec,
reliability 255/255, txload 71/255, rxload 255/255
What means 255 after / ?
The Cisco IOS calculates the loading by dividing either the input or output rate by the bandwidth and multiplying by 255. In your case, the bandwidth set on the interface is 512, hence the txload (output rate) is 71 / 255 * 512 = 142kb/s, and the rxload (input rate) is 255 / 255 * 512 = 512kb/s. These values can be crosschecked by the line on the show inerface that gives the 5 minute rate average.
Note that if the wrong bandwidth is configured on the interface, the rxload and txload will not be accurate. And the ratings of these are always against 255.