That’s the Sentencing Project’s estimate of state-level felony disenfranchisement. Read the study here:

“A record 6.1 million Americans are forbidden to vote because of felony disenfranchisement, or laws restricting voting rights for those convicted of felony-level crimes. The number of disenfranchised individuals has increased dramatically along with the rise in criminal justice populations in recent decades, rising from an estimated 1.17 million in 1976 to 6.1 million today.”