I'm looking for the most readable quantitative explanation, with the least amount of difficult mathematics. Rather than an answer with just a number, I'd like to see the derivation from the CKM matrix.
A clear recent review of flavor physics, including CP violation, is in the TASI lectures by Gedalia & Perez. The parametrization-independent measure of how much CP violation is present in the Standard Model is called the "Jarlskog invariant"; it's explained in those lectures, but might be a useful keyword if you're searching for other resources. If you want to understand why the observed CP violation is insufficient to explain the baryon asymmetry we observe in the universe around us, you might try these lectures on baryogenesis by Jim Cline.