Impossible. Syringes are marked by cc's/mls which are measures of VOLUME
MG is a measure of WEIGHT which doesn't not correlate to any sort of indication on a syringe since each compound has a different concentration.
You can have 1ML = 200mgs, 300mgs, 500mgs depending on the concentration of the substance.
I think you are confused and confusing the OP more than necessary.