|I actually purchase the large when my ds outgrew the mediums, he was around 18 lbs. I was thinking that I could skip the M/L and actually I could have because the large fit fine, I just didn't like the puffiness. He is now 23lbs and is still wearing the M/L and I like the way they fit better. He has been in them for 5 months, he is certainly getting more use of them then I thought he would. It is just my preference, there was nothing wrong with the fit of the large they did what they were suppose to do.