With UDFAs getting signed and camp starting, KC's resident stats man, Martin Manley recently made a post about UDFAs, how important they are in the NFL, how many are in the NFL, and what % of team rosters they make up (as well as on the Chiefs). Here are some meta-calculations from it:
1. On average UDFAs make up 37% of league rosters
2. UDFAs made up 60% of the Rams team in 2011
3. 30% of the Chiefs roster last year were UDFAs
It's a good read that I recommend checking out.