The number of rounds in your draft is equal to the total number or roster positions (starting + bench) that have been created in your league.

From your league overview page, you can click the "Settings" link to view the league settings in place in your league.

Your league roster configuration is displayed in the "Roster Positions" line of the league settings. So, if your league features 10 starting roster positions and 6 bench (BN) positions, your draft consists of 16 rounds.