From Wikipedia: "The concentration of active psilocybin mushroom compounds varies not only from species to species, but also from mushroom to mushroom inside a given species, subspecies or variety. The same holds true even for different parts of the same mushroom. In the species Psilocybe samuiensis, the dried cap of the mushroom contains the most psilocybin at about 0.23%–0.90%. The mycelium contains about 0.24%–0.32%."

So for 3.5g ≈ [8.05mg ; 31.5mg] And for 2.5g ≈ [5.75mg ; 22.5mg]

It seems to be in the typical range for a medium to strong dose. A simple glance at the wikipedia page suggests that Psilocybe cubensis is ~1% pysoactive ingrediants (psilocin and psilocybin) so, working backwords, 25mg psilocybin would be about 2.5g worth of mushrooms.

I haven't taken into account how psilocin & psilocybin are different or if there is typically degredation of the psychoactive compounds typically prior to ingestion (during transportation, handeling, etc.)