sorority house size

It varies from house to house. Each house has a quota that they are supposed to meet, some meet it and some don't. Most people who finish the recruitment process get bids, the people who don't are usually the ones who drop out sometime during the week or suicide rush. That means that on pref day they only put one house out of the two that they went to and would not like to be considered for the other house. But usually pledge classes are in the low 100s range.

Quota is the number of girls who attend preference divided by the number of houses. (12)

If you pref 2 houses and do not suicide, you are essentially guaranteed a bid.

However if you only have 1 house on pref, or if you decide to suicide, you won't be eligible for quota additions which makes it more likely to receive a bid.

Pretty much every house every year makes quota plus, so if you make it to pref day, you'll make it to bid day. It just might be your second choice. Or not.