How many cc is in 4 mg?

There is no direct conversion. The number of cubic centimeters in one, or four milligrams depends on the density of the material being assessed. Cubic centimeters (cc) is a measure of volume. Milligram (mg) is a measure of mass.

For pure water at 20 C, and only for that liquid, one 4 mg occupies a volume of 4 cc.