  Recently, compressed H$_2$S has been shown to become superconducting at 203 K
under a pressure of 155 GPa. One might expect fluctuations to dominate at such
temperatures. Using the magnetisation critical current, we determine the
ground-state London penetration depth, $\lambda_0$=189 nm, and the
superconducting energy gap, $\Delta_0$=27.8 meV, and find these parameters are
similar to those of cuprate superconductors. We also determine the fluctuation
temperature scale, $T_{\textrm{fluc}}=1470$ K, which shows that, unlike the
cuprates, $T_c$ of the hydride is not limited by fluctuations. This is due to
its three dimensionality and suggests the search for better superconductors
should refocus on three-dimensional systems where the inevitable thermal
fluctuations are less likely to reduce the observed $T_c$.
