>a chapter is supposed to convey a entire piece of a story,
When I write, this is exactly my goal at determining the chapter boundaries. But still, i aim for 25k characters (an optimal size giving a decent balance between the release rate and my control over the story). If my chapter bloats out of control, I usually cut it in half.
A few years ago when I was more prolific, having more free time, I aimed for a 50..60k characters per chapter.
But still, the chapter size ususlly varies according the author's muse along the story.
Note: as a part time translator, I dislike the word count, because it differs significantly between the equal English and Russian texts while the character count stays quite consistent).
Also, the official way is counting characters (except spaces), and the book volumes and payments are counted in the standard units called "auctorial sheets" comprising of 40.000 characters. If you open any book, in its technical data you'll find its volume counted in "conventional auctorial sheets". This system is used for at least half a century, AFAIK.
At least, this side of Atlantic.
HTML and other formats are always inflated numbers due to fact the formatting inflates the file size. Thus 100kb TXT is more to read than 100kb of HTML.
You should *not* use a HTML size in bytes. It could have been created with M$ Word, for all you know, which adds a mammoth formatting overhead.
Furthermore, *I* can't use the TXT size in bytes anymore! Becaue the modern encoding is Utf-8, which makes it two byter per a Russian character.
The only way to get a meaningful numbers nowadays is to past the chapter into Word (OpenOffice, etc.) and summon the statistics menu.