How many lines should a function have at most?

Question

Is there a good coding technique that specifies how many lines a function should have ?

Answer 1

No. Lines of code is a pretty bad metric for just about anything. The exception is perhaps functions that have thousands and thousands of lines - you can be pretty sure those aren't well written.

There are however, good coding techniques that usually result in fewer lines of code per function. Things like DRY (Don't Repeat Yourself) and the Unix-philosophy ("Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface." from Wikipedia). In this case replace "programs" with "functions".

Answer 2

I don't think it matters, who is to say that once a functions lengths passes a certain number of lines it breaks a rule.

In general just code clean functions easy to use and reuse.