  A power law is postulated for both site and bond percolation thresholds. The
formula writes $p_c=p_0[(d-1)(q-1)]^{-a}d^{\ b}$, where $d$ is the space
dimension and $q$ the coordination number. All thresholds up to $d\rightarrow
\infty$ are found to belong to only three universality classes. For first two
classes $b=0$ for site dilution while $b=a$ for bond dilution. The last one
associated to high dimensions is characterized by $b=2a-1$ for both sites and
bonds. Classes are defined by a set of value for $\{p_0; \ a\}$. Deviations
from available numerical estimates at $d \leq 7$ are within $\pm 0.008$ and
$\pm 0.0004$ for high dimensional hypercubic expansions at $d \geq 8$. The
formula is found to be also valid for Ising critical temperatures.

Condensed Matter