Psychedelics Daily has created a multi-species psilocybin mushroom dosage calculator that can be used to determine the proper dosage for various species of psilocybin mushrooms.
This is helpful because potency can vary widely from one species to another. However, since the potency can also vary across even a single species depending on growing conditions, moisture content, feeding material, and other variables, this calculator is an approximation.
The calculator also includes guides on preparing microdoses of magic mushrooms, things to know about psilocybin mushrooms, and information about how they might be the cure for migraines. I encourage you to check out this resource and share it with the psychonauts you know.
Image by fractal_ken, courtesy of Creative Commons licensing.