By Ezra Klein and Evan Soltas

Here’s a bit of context for Attorney General Eric Holder’s decision to encourage federal prosecutors to charge low-level drug offenders with less severe crimes (thanks to Dylan Matthews and Brad Plumer for doing a lot of the spade work here):

– The U.S. prison population is more than 2.4 million.

– That’s more than quadrupled since 1980.

– That means more than one out of every 100 American adults is behind bars.

– About 14 percent of the prison population is in federal prison — that’s the group Holder is talking about.

– The single largest driver in the increase in the federal prison population since 1998 is longer sentences for drug offenders.

– The average inmate in minimum-security federal prison costs $21,000 each year. The average inmate in maximum-security federal prisons costs $33,000 each year.

– Federal prison costs are expected to rise to 30 percent of the Department of Justice’s budget by 2020.

–  Sens. Dick Durbin, Pat Leahy, Mike Lee, and Rand Paul have all endorsed legislation to give federal judges more flexibility when sentencing non-violent offenders. Holder backs the bill, too.

– The most serious charge against 51 percent of those inmates is a drug offense. Only four percent are in for robbery and only one percent are in for homicide.

via Wonkbook: 11 facts about America’s prison population.