Consider the type of event you are hosting to adequately determine how many people you can fit at a table. The chart below is a general guide to help in your decision making.
For example, if your event is business oriented where people may need work space to set up laptops, binders, etc, then you may want to give people more room and figure a minimum number of people per table. Also, in regards to banquet tables, take into consideration whether people will be sitting on both sides of the table and/or at the ends. And finally, don't try to cram too many people at any type of table -- they will surely appreciate it!