You cannot. Micrograms per centimetre cubed is a measure of density, with dimensions [ML-3] whereas micrograms is a measure of mass with dimensions [M]. They measure different things and elementary dimensional analyses teaches that you cannot convert between measures with different dimensions.
There are 1000 micrograms in a milligram. You have to divide here to convert. 300ug/1000 is 0.3 milligrams.
There are 0.3mg in 300 micrograms.
0.3 mg = 300 micrograms
There are 1000 micrograms in a milligram. Therefore 10 milligrams is 10,000 micrograms. 300 micrograms is 0.3 milligrams. 10-0.3 is 9.7 milligrams.
There are 1000000 nanograms in a milligram. Therefore 300 nanograms is 0.0003 milligrams.
There are 1000 milligrams in a gram. Therefore 2.3mg is 0.0023 grams
To convert 300 mg to 2000 IU you need to first convert the milligrams to micrograms (1,000 mcg is equal to 1 mg). Next, you need to determine what one IU represents.
30 cm 1 centimeter = 10 millimeters 1 millimeter = 0.1 centimeter
There are 1000 micrograms in a milligram. Therefore 300 micrograms is 0.3 milligrams.
300mg equates to 300,000 micrograms (mcg) *(1000mcg per mg).
There are 1000 micrograms in a milligram. So you need to multiply by 1000 here. 0.3x1000 is 300 micrograms.
Convert to a common unit, then compare! Note that 1 centimeter = 10 millimeters.