Hausdorff dimension is a method of measuring the dimension of a metric space. It is always a non-negative real number, but it need not be an integer; one way to define a fractal is a metric space with a fractional (non-integral) Hausdorff dimension. Hence Hausdorff dimension is an example of fractal dimension.

The Hausdorff dimension of the cartesian space$\mathbb{R}^n$ (or any inhabitedopen subset thereof) is $n$. The Hausdorff dimension of a self-similar fractal which consists of $n$ copies of itself reduced in size by a factor of $m$ is $\log_m n$.

In general, Hausdorff dimension may be defined using Hausdorff measure?.