How many people can you expect to RSVP “no"?
You should expect that 20% of your invitees to be unable to attend. If many of your guests are from out of town, that may be a low estimate. However, you should always avoid the temptation to over-invite in expectation that a certain number of people won’t be able to come, because you may be pleasantly surprised at how many people put forth the effort to make it to your wedding. It’s better to only invite the amount of people you can actually accommodate, and then rely on a “B list” to fill in any gaps.
Cegielski, Jennifer. Wedding Invitations. New York: Stewart, Tabori & Chang, 2004. Print.