mg/m2 is the milligrams of hydrocortisone per meter squared of body mass. It allows you to compare how much medicine a person is getting even though their weight and height are changing. The easiest way I have found to calculate it is to go to a web site http://medicine.ucsd.edu/cystinosis/bodysurface.htm and enter in the person's height and weight. It will automatically give you the m2. Then take the mg per day and divide it by the m2 to get the mg/m2. For example a height and weight of 33 3/4 inches and 30.2 pounds gave a m2 of .578. 8.75 mg of cortef tablet a day divided by .578 = 15.14mg/m2 If you would like more info on mg/m2 let me know and I can look up this article I have that discusses it all.