Title length and number of tabs determine tab size, so keep words to a minimum, using commonly accepted abbreviations when possible.  If a large number of tabs is needed, you may want to arrange them in more than one bank" or row of tabs in consecutive order from top to bottom. 

For example, 20 tabs may be arranged in 2 banks of 10 tabs, 4 banks of 5 tabs, or 5 banks of 4 tabs. 

The ½" extension is the most popular size for ring binders.   And when titles on this size tab need only one-line titles, a larger and bolder type face may be used. 

Keep in mind that your reader's interest is kept up by organizing clearly; if you put too much information in one category, you're likely to lose that interest.  So add more sections to keep it moving!