This page will help when estimating monthly bandwidth usage. Of course, it's only an estimation because the output depends on the 'best guess' when entering data.
For a web page, it's just the total file size for all the .html, .txt, images, sounds, etc that are included in the page .. x .. times the number of views.
However, when you (or others) load / post your files (such as images, sounds, etc) on another site (such as a forum) then those larger files can really increase the bandwidth usage.
Just as an example, the default values are from a web page (10KB) with about 100 visitors a day (3000/month). The web page has two images (50KB and 12KB). And there was 1 image (137KB) that was posted in a forum message and viewed by 290 people a month.
VIP: reminder - a file size of 1024000 is 1000KB (or 30000 is about 30K). In other words, many people enter the wrong value i.e. they enter a value about 1000 times too high. Use KB for file size input! ! !
BTW: leave out comma's e.g. enter 30,000 as 30000