# Math Help - Lebesgue measure and Hausdorff dimension

1. ## Lebesgue measure and Hausdorff dimension

Let $E\subset\mathbb{R}^{n}$ be a set that is not measurable with respect to the n-dimensional Lebesgue measure. Show that $E$ has Hausdorff dimension n.

2. ## Re: Lebesgue measure and Hausdorff dimension

Assuming that the Hausdorff dimension is the number $s= \inf_{t} \{ \mathcal{H}_t(E)=0\} = \sup_t \{ \mathcal{H}_t(E)=\infty \}$, then we have $\mathcal{H}_{s'}(\mathbb{R}^n)=0$ for all $s'>n$ (To see this note that the s'-Hausdorff measure of an n-cube is zero for $s'>n$ and use subadditivity of the outer measure), and by monotonicity $\mathcal{H}_{s'}(E)=0$, so $s\leq n$. If $s then $\mathcal{H}_n(E)=\lambda_n(E)=0$, but Lebesgue measure is complete so $E$ is measurable, a contradiction.