jmc

Since we defined $g(x)=h\left(\frac{x}{2}\right)$, a real number $x$ is in the domain of $g$ if and only if $\frac{x}{2}$ is in the domain of $h$. Therefore, the domain of $g$ consists of all $x$ such that $$-8\le \frac{x}{2}\le 8.$$The solutions to this inequality are given by $-16\le x\le 16$, so the domain of $g$ is an interval of width $16-(-16)=\boxed{32}$.