It is shown that a dimension-invariant form D(d) = bd(gamma) for fractal di
mension D of random systems (where d is Euclidean dimension of the embeddin
g space) is in good agreement with results of numerical simulations perform
ed by different authors for critical (p = p(c)) and subcritical (p < p(c))
percolation, for lattice animals, and for different aggregation processes.