I usually plan on 2 per person... I seldom have any left over. Some will eat 2 others may not eat any.. Then if they're like MY family... Some may eat several.... Leave any left over after the meal available with butter and an assortment of jams, and they will get eaten up.
150 figure half of the 100 will eat 2
If you are inviting 125 people, the minimum number of rolls you can have is 125. But it is always good to keep some extra in case somebody wants to eat more than one. If, let's say, 50% of the people take 2 rolls each and the rest take 1 roll each, on an average you will need to have 187.5 rolls. So I suggest you keep 188 rolls, and then by the end of the day, if you are left over with some, you can eat them all on your own!
If they are anything like my boyfriends family make sure you have at least 2 for each person maybe even 3 each. His family can eat 3-4 each, but I'm not a bread person I usually only eat one to be polite.