3iu equals 1 mg. if your off by an iu or 2, its not exact science. how does the serono pen come anyway? ive never seen it. used to have the genotropin pens , the ones you twisted and the liquid mixed with the powder. thinking back they were a bitch to figure out too cuz they contained something like 1.78 cc with 17 iu or something. maybe im wrong though, this is years ago. i do remember that i was using nolvadex off and on when i had a bunch of these(pens). then later they said nolvadex kills the gh. shit. anyway they used to come in these weird plastic containers.....i used to look at them stacked in my little refridgerater and get excited. its always like that with a new drug. its like a new chuchu train or sand shovel when your a kid-fun to fuck with for awhile then you moveon. hope that helped somehow