Yeah, I think that was a general estimate I found some supporting research for a few years back when I looked into it a bit, and I've seen similar quoted elsewhere.

It's not easy to come up with an accurate number at all due to all the different state systems not being perfectly comparable, treating different things in different ways, and duplicating individuals who have convictions in more than one state. Even attempts to link them together have been incomplete and inaccurate.

I'm not particularly surprised at that level, though... it's going to include _lots_ of low-level things that are technically classified criminal even though they're often just a ticket: kids caught with beer at a party, speeding in areas that have a "20 over the limit" rule that automatically upgrades to a higher offense, failure to pay tickets that gets escalated to a court, etc...