Yes, using the conversion formula \[1\ mg\ \ =\ \ \frac{1}{1000}\times 1\ g\] , “55mg” can be converted to corresponding “g” in the following way.

\begin{aligned}

  1 m g & =\frac{1}{1000} \times(1 g) \\

\therefore 55 m g & =55 \times(1 m g) \\

& =55 \times \frac{1}{1000} \times(1 \mathrm{~g}) \\

& =0.055 \mathrm{~g}

\end{aligned}

So, there are “0.055g” in “55mg”.