In order to convert from grams to milligrams, we need to know that 1 gram is equal 1000 milligrams.
Then, to find how many mg is 12.3 g, we can use a rule of three:
[tex]\begin{gathered} 1\text{ g}\to1000\text{ mg} \\ 12.3\text{ g}\to x\text{ mg} \\ \\ \frac{1}{12.3}=\frac{1000}{x} \\ 1\cdot x=12.3\cdot1000 \\ x=12300 \end{gathered}[/tex]So 12.3 g is equivalent to 12,300 mg.
