There seems to be no hard and fast rule for margins or line length, but here’s what I’ve come up with.
In order of importance, you’re looking at:
font size > readability > line length > column width > margin
So first choose your font size.
The most readable line length is 40–90 characters, including spaces (regardless of font size).
There is a “points-times-two line length rule”, which says you take the type size in points, then double it to find the ideal line length in picas. I don’t use picas but metric, so this would be:
font size x 4.2mm = line length
If the answer falls within the 40-90 characters then it’s good to go. In general, the 40-90 characters works as a good guide, anything within that works.
Then adjust column width and margins to fit the best line length
If this doesn’t work out (for example, you have a set page size and this layout doesn’t fit) try changing the font size.
Other things to keep in mind:
- The smaller the point size of the text, the larger the page margins will need to be.
- Shorter lines are more comfortable to read than longer lines.You can check line length using word count (select the text then Window > Info or press f8).
- The bottom margin should be larger than the top margin, if both margins are the same the text looks like it is sliding of the bottom of the page (5mm is fine as a starter for most magazine/book layouts).
- Readability is of paramount importance for long text, for a novel or long magazine article. If you’re doing diagrams, or short blocks of text (in a brochure say) it’s not so vital.
- Big, generous margins = Classy, elegant, formal. Thin margins = Low quality, mass produced (like in newspapers, tacky brochures etc).
Again, there seems to be no set answer, but for best readability (可读性) it should be around 28-30 characters per line. An example given was 9-10cm for 11pt text, with columns no shorter than 4cm. For 11pt text, 14-15pt leading is recommended.