What are the general rules for heights/widths of punctuation marks when designing a font?

Question

I've been getting into font design recently, and I'm pretty clear on the various widths and heights for the letters, but I realized I'm at a loss when it comes to punctuation. I can kind of guess that certain things like an exclamation point or a parenthesis would go all the way to the cap height, but how big should a period or a comma be, or how wide should an underscore be? I have questions for pretty much every punctuation mark.

Are there rules or guidelines for the various marks, or is it just whatever looks right?

Answer 1

I asked a similar question about designing certain special characters and there are some good resources and methods in the answers there that should help you.

The best advice I can give is to study existing typefaces. Look at well made typefaces, open them up in a font editor and inspect the metrics and placement of the glyphs you're interested in. There are general rules for the shapes and placement of glyphs (not only punctuation) but no two typefaces will be the same, so don't focus too much on specific numbers, look at a wide variety of fonts and just try to get a feel for how they are designed, paying attention to alignment etc...

I'd also say that as long as your glyphs are understandable, readable and follow the generally accepted design paradigms, the most important thing is that the design is consistent with the design of the typeface as a whole.

If you're unsure about a specific character then you can ask a question on this site; whether you ask about designing a character in general or want a critique on your design. Some previous questions of mine for example:

• How to design the letter ß (eszett or sharp S)
• Is this Dutch IJ ligature suitable and readable to native speakers?

As for specific resources...

A resource I often use is Microsoft's Character Design Standards, which gives you an idea of placement and metrics for a lot of characters. They have a specific section on punctuation, which should give you a good idea of where to start.

For diacritics see When designing a latin-based typeface, how are diacritics handled?, which has a lot of good resources; most notably (another I often use) The Diacritics Project.