You can have up to 50 people in your group at a time. We've found that the best group size is 4-10. 

Remember, GroupMe is reply-all by default; whenever anyone in the group sends a message to the group, the message will go to everyone. There is no way to change this, and it's central to the GroupMe experience.

With that in mind, if you have a group that needs more than 50 people in it and you're looking for a reply-all solution, submit a request and we'll see what we can do.