Ignoring the embarrassing and undemocratic concept of Superdelegates, which are not bound and often change their votes to support whoever won the most pledged delegates, there are a total of 4,051 delegates in the Democratic primaries. In order to secure the Democratic nomination, a candidate needs to win at least 2,026 delegates.
At this point, Hillary Clinton has won 1,175 delegates and Bernie Sanders has won 856 delegates. So Hillary has a lead of 319 delegates. 2,020 delegates, close to half, remain to be allocated between now and June 14.
In order to secure the nomination, Hillary Clinton needs to win 42.13% of the remaining delegates.
In order to secure the nomination, Bernie Sanders needs to win 57.92% of the remaining delegates.