Mushroom (and other entheogenic) dosage can greatly vary from person to person and from one mushroom to another... it also depends on what kind of mushroom you ingest. Some shrooms are much more potent than others. Cubensis, the most common magic shroom, while potent, is not even close to the most potent magic mushroom. Still, since Cubes are so popular, suggested dosage will be for Cubensis.
Use the Shroomery Dosage Calculator if you wish to calculate a recommended dosage for another shroom species. But be prewarned, dosage can vary GREATLY from person to person.
Knowing a thing or two about TripLevels may prove helpful as well. People with a higher (or lower) than average tollerance, can sorta' figure out their own personal dosage scale with the help of the TripLevels.
For first time trippers:
(All dosage amounts are for Cubensis. For other species and suggested dosage, check the Shroomery Dosage Calculator.)
It is recommended (by many) you eat between .75 and 1.5g grams of dried Cubensis for your first trip, without the addition of a MAOI. Usually, .75 - 1.5g is perfect. More than 2g may be asking for trouble. Some people suggest a dose as low as .25g, but any dose less than that is imperceptable in most humans.
Some people will say 1.5g is not very potent. And true, 1.5 grams may be a disappointingly mild trip. It could also be surprisingly strong.
Remember, different people have different reactions to mushrooms. If you have never tripped, how do you know how you'll react?
With the proper set and setting, .75 - 1.5g a fine suggested first dose. Without the proper set and setting, don't even bother tripping.
A person with a LOW psilocybin tolerance will trip on 1.5g like they ate 4.5g or more (which is a very large dose for an unsuspecting newbie). This is true. Many Shroomerites have very LOW tolerances. Some people are very sensitive to psilocybin. It is best to start small, to make sure you know your tolerance. Besides, the VAST majority of first time trippers will have their minds expanded on 1.5g whether they have a high tolerance or not.
On the other hand, some people have a HIGH tolerance to psilocybin and they will not trip as much on 1.5g as most people.
It is better to be safe than sorry. Start small, find your tolerance, then work up to a higher dose... if you wish. There is nothing wrong with keeping your dosage small. Small doses gone bad, are much less mentally traumatic than large doses.
Most experienced trippers take between 1.5 grams and 3.5 grams for what they'd consider an "Average" trip. It is not recommended that somebody exceed this recommended .75 - 1.5g dosage until they're familiar with, and know how to take control of the trip experience. Even then, large doses of shrooms can be awe-inspiringly frightening.
As for hallucinations.
You can trip on a pretty small dose, but hallucinations are more noticeable with medium to large doses. Don't expect to hallucinate too much on a small dose, you may be disappointed. Hallucinations are not as important as many first time trippers have been led to believe. Until you understand tripping and tolerance, stick to small doses. You'll still have a great time. Some people just see more stuff than others.
First time trippers benefit from taking doses that aren't likely to induce hallucinations. You can find your bearings at this level; you begin to feel a buzz and you can't quite put your finger on it. Then, when you wish to elevate your experience, you are familiar with the mushroom-trip sensation. This is most beneficial to enjoying hallucinations. Discuss at The Shroomery BB