The number of peak concurrent users (Npeak) the server needs to handle.
The average request size on your site, r. The average request can include multiple documents. When in doubt, use the home page and all its associated files and graphics.
Decide how long, t, the average user will be willing to wait for a document at peak utilization.
Then, the bandwidth required is:
Npeakr / t
For example, to support a peak of 50 users with an average document size of 24 Kbytes, and transferring each document in an average of 5 seconds, requires 240 Kbytes (1920 Kbit/s). So the site needs two T1 lines (each 1544 Kbit/s). This bandwidth also allows some overhead for growth.
The server’s network interface card must support more than the WAN to which it is connected. For example, if you have up to three T1 lines, you can get by with a 10BaseT interface. Up to a T3 line (45 Mbit/s), you can use 100BaseT. But if you have more than 50 Mbit/s of WAN bandwidth, consider configuring multiple 100BaseT interfaces, or look at Gigabit Ethernet technology.