When a diode is properly forward biased what is the voltage drop across it equal to?

The forward biased voltage drop of a diode depends on the type of diode and the current through the diode. A typical silicon diode will exhibit a voltage drop between 0.6v and 1.4v depending on current. An LED might range from 2v to 3v. A germanium diode might go a low as 0.2v. Bottom line; it varies.