One of the first things that you'll do as part of wedding planning is to choose your ceremony and reception venue(s). As exciting as venue searching is, one of the things that will determine whether you can or can't use a venue (besides budget!) is the number of people on your invite list. It's okay to research, visit and shortlist your venues, but you also need to finalize your invite list before committing to a venue. A lot of newly engaged couples have a number in their heads about how many people they'll be inviting, but until they actually start writing down all the people they want to invite, that original number is usually a lot lower than the invitation list.
A general rule is the number of invitations you send out is about the total number of people that will RSVP for your wedding. For instance, if you send out 100 invitations that invites a total of 175 people, you will likely get around 100 total people (plus or minus 10%) that RSVP. Obviously this is a general rule and some factors will affect the number; things like whether your invitees are mostly from in town (likely will have more people RSVP) or if you're having a destination wedding (likely will have less people RSVP). No matter what the situation, just make sure that you're overestimating the number of potential RSVPs when you decide on your final venue.
This is a good rule to help you estimate whether the venue you've fallen in love with will even be close in having the necessary capacity to house your family and friends as they celebrate your special day with you!
