The chart applies to dried mushshrooms having 1% psilocybin by weight. It's based on an average or medium adult dose being 25mg. Therefore, 25mg/1%= 2.5g of dried shrooms. It can apply to other species but is intended primarily for the Cubensis variety. Sensitivity to the molecule varies so you have to experiment a bit to test yours.
Actual potency of the mushroom varies in nature from zero up to almost 2% for some. It's best to start with a small dose like 0.5g to see what that does. Then, over the course of a few weeks, work your way up to the dose you like in 0.5g increments. This way you won't over-do it, and you'll have a better idea what to expect.
If you've never done them before it's a good idea to have someone around to keep you safe.