What does 0.8 mg equal to cc?

This is difficult because milligrams (mg) is a unit of mass, and cubic centimeters (cc) is a unit of volume.

It can be done if you know what you are measuring. For example, let's use water. Water has a density of 1gram/cc, so it's easy to calculate with. So, for water 0.8mg = 0.0008cc (= 0.8 cubic millimeters), since 1000mg = 1 gram.