I'm thinking here of one of the deleted scenes where Sonny calls Tessio and asks him to send over 50 good men. That and the scene where Clemenza asks about all the new faces and is told they're there because they had hit Bruno Tattaglia. That got me thinking just how big was don Vito's Family. Anyone have an idea?

Strictly speculation but:

Sonny tells Tom: "One hundred button men on the streets...if Solozzo shows a hair on his ass, he's dead." I assumed he meant almost the family's full strength in addition to the 50 at the Mall (assuming he kept all 50 at the Mall after he found out that Paulie was the traitor).

As for recruiting new people: Perhaps Michael and Vito let their numbers go down after Vito retired--the better to make the other families think they were slippin'. And maybe the new "secret" regime was meant to bring back strength for the Great Massacre.

All in all, I will GUESS that the Corleones didn't have more than 200 - 250 made men.

OK TB. But here we have to go to the novel again. What about Sonny's boast that Clemenza and Tessio can match all the five families gun for gun?

I agree, but I also don't see how they could have had anything less, considering they were the strongest of the Five Families. In the novel Clemenza also states that they outnumber the other four families and that they could muster a thousand men; I think that was their entire criminal work force including associates. Also bear in mind that even in times of war, there still need to be men left to look after the rackets. So Sonny's statement probably didn't include the entire family.