Number of guests for your event.
Graduation parties are often setup as an open house type event or as a specific meal time event. Now is the time you will need your guest list.
An open house type graduation party is when your guest are going to come and go throughout your event. Food and snacks are provided throughout the entire event. For an open house type graduation party plan on seating about half of the guests you invite. Remember young children may not sit down long enough to count and the graduates friends may only be at the party a short time because they have 5 more parties to go to on that day. On the other hand relatives if they come may be there for a long while.
A graduation party where there is a specific meal time (dinner served between 6-6:30) may require you to have more seating because guests are very likely to come in that small window. Plan on seating 60% to 80% of the guests you invite.
Maximum number of guests I plan to seat at any one time.