How do you convert the volume of hydrogen gas from mL to L?

$\text{Multiply by}$ ${10}^{-} 3$
$1 \cdot L \equiv \frac{1 \cdot \cancel{L}}{{10}^{-} 3 \cdot \cancel{L} \cdot m {L}^{-} 1} = \frac{1}{10} ^ - 3 \times \frac{1}{m {L}^{-} 1} = 1000 \times \frac{1}{\frac{1}{m L}} = 1000 \cdot m L$,
And thus, to get a volume in $L$, multiply volume in $m L$ by ${10}^{-} 3$..........