There are currently 36 states (and the District of Columbia) with marriage equality, so the ruling by the Supreme Court would likely strike down the bans in the 14 remaining states.
The specific question the Supreme Court will ask parties to address in briefs and oral arguments are:
1) Does the Fourteenth Amendment require a state to license a marriage between two people of the same sex? 2) Does the Fourteenth Amendment require a state to recognize a marriage between two people of the same sex when their marriage was lawfully licensed and performed out-of-state?It is likely there will be oral arguments in April (90 minutes on Question 1, 60 minutes on Question 2) and a final decision issued in the case(s) by June 2015.
Hat/tip to Chris Geidner!