milligrams is a measure of mass and milliliters is a measure of volume for fluids. To convert milligrams to milliliters you need to know the density of the fluid.
The Greek letter ρ is often used...
milli means 1 thousandth, 1/1000. 1 x 10-3 g micro means 1 millionth, 1/ 1000000. 1 x 10-6 gWhat is meant by a micro milligram? A millionth of a milligram? That is 1 x 10-9 g. A nanogram.