[StickmanDave]

Originally Posted by tbaroghel

Yes please, give us a "quick-guide" on how to fix font, fontsize and margins for ePub using Calibre. I am sure this will be a hit!

The calibre manual has this to say:

One of the nicest features of the e-reading experience is the ability to easily adjust font sizes to suit individual needs and lighting conditions. calibre has sophisticated algorithms to ensure that all the books it outputs have a consistent font sizes, no matter what font sizes are specified in the input document.

The base font size of a document is the most common font size in that document, i.e., the size of the bulk of text in that document. When you specify a Base font size, calibre automatically rescales all font sizes in the document proportionately, so that the most common font size becomes the specified base font size and other font sizes are rescaled appropriately. By choosing a larger base font size, you can make the fonts in the document larger and vice versa. When you set the base font size, for best results, you should also set the font size key.

Normally, calibre will automatically choose a base font size appropriate to the Output Profile you have chosen (see Page Setup). However, you can override this here in case the default is not suitable for you.

The Font size key option lets you control how non-base font sizes are rescaled. The font rescaling algorithm works using a font size key, which is simply a comma-separated list of font sizes. The font size key tells calibre how many “steps” bigger or smaller a given font size should be compared to the base font size. The idea is that there should be a limited number of font sizes in a document. For example, one size for the body text, a couple of sizes for different levels of headings and a couple of sizes for super/sub scripts and footnotes. The font size key allows calibre to compartmentalize the font sizes in the input documents into separate “bins” corresponding to the different logical font sizes.

Let’s illustrate with an example. Suppose the source document we are converting was produced by someone with excellent eyesight and has a base font size of 8pt. That means the bulk of the text in the document is sized at 8pts, while headings are somewhat larger (say 10 and 12pt) and footnotes somewhat smaller at 6pt. Now if we use the following settings:

Base font size : 12pt
Font size key : 7, 8, 10, 12, 14, 16, 18, 20

The output document will have a base font size of 12pt, headings of 14 and 16pt and footnotes of 8pt. Now suppose we want to make the largest heading size stand out more and make the footnotes a little larger as well. To achieve this, the font key should be changed to:

New font size key : 7, 9, 12, 14, 18, 20, 22

The largest headings will now become 18pt, while the footnotes will become 9pt. You can play with these settings to try and figure out what would be optimum for you by using the font rescaling wizard, which can be accessed by clicking the little button next to the Font size key setting.

All the font size rescaling in the conversion can also be disabled here, if you would like to preserve the font sizes in the input document.

A related setting is Line height. Line height controls the vertical height of lines. By default, (a line height of 0), no manipulation of line heights is performed. If you specify a non-default value, line heights will be set in all locations that don’t specify their own line heights. However, this is something of a blunt weapon and should be used sparingly. If you want to adjust the line heights for some section of the input, it’s better to use the Extra CSS.