The bandwidth is a fractional reserve. Basically (simplified): The steem network has an amount of bandwidth available and gaves you some of that, respective to your steem power. You can use that bandwidth. But if people use the bandwidth, there is less available, so steem will give less out.
Example: Say I have one GB available. And I do a huge post that cost me 3 MB. That post reduces the network overall supply and I have used 3MB of 500MB. If I do another post, I have used 6MB of 250 MB. And if I wait a bit, the network has less load again and I have 6MB of 1GB again.
So: How much bandwidth actions cost, that is pretty fixed. But how much is available in the system is always in flux. Similar to how voting power is pretty easy to calculate, but determining how much your upvote is worth is pretty complex and changes all the time.
So while timcliff and many others know how it works, explaining it is not easy. And since the maximum is system dependent, there is no easy way to show it per user.
I am also experiencing the bandwidth problem 4-5 days.And I don't know what the cause is.You said related to what we do on the site.but I did not do any operation for 15 hours, compared with the bandwidth error of the band.So I did not fully understand why ?
Thanks for information. @reggaemuffin