From my experience, Mitchell and Ness jerseys are usually fairly accurate with regards to their number sizes (a size 46 would generally mean approx. 46 inches around the chest). There are always subtle variations. For instance, the M&N size 44 and the M&N size 46 are virtually the same jersey -- they seem to have the exact same chest measurement, though the 46 is slightly longer. I always use the rule of thumb that if there is ever a shadow of a doubt, to err on the high side. Worst case, the jersey is too long and can be take in at the bottom.

On the contrary, the Majestic "authentic" jerseys are ridiculous. A retail size 44 Majestic measures a whopping 50 inches around the chest. Why such a huge disparity? I have team issued/game used Majestic jerseys in sizes 46 and 48 that are SMALLER than their retail 44s. I suppose if you base M&N purchases on your knowledge of these, you will always buy the wrong size ;-)