really depends on the mushrooms and how hard you want to trip. first time, i took 1/8 and i was fucking GONE. next time i did them, i took 2g and that was way more along the lines of what i was looking for in a trip. i wasn't outside talking to pinecones and shit. if its your first time and you dont want a very extreme trip and mushrooms are readily available, i'd say start out small with only a couple grams. if you like that, then you can move up to doing 1/8 or more. have fun