The number of tables depends on the number of guests, your budget and whether there are other events going on at the same time. If you have a disco we would say divide the number of guests by two. This will likely be the number you wish to entertain at the gaming tables at any one time. 10 - 15 players can play around a table at a time.
Therefore if you were entertaining 120 guests with a disco or band in addition to the fun casino, you would divide 120 by two and then by 15. The result is that the number of tables you would likely need is four.
This is only as a rough guide - if you were just having a fun casino you may like to have more tables. In any event, we are happy to offer expert advice on which games to have and how many to ensure your evening is a success.