My examples are a little different. My image emphasizes coins which are the same denomination and type, but, nevertheless, different sizes. They are a type where it is helpful to have the maximum diameter stated in mm. Here are two Byzantine anonymous folles of Class A2, attributed to Basil II and Constantine VIII, 976-1025. The one on the left is 35 mm and 19.76 grams. The one on the right is 28-26 mm and 11.28 grams. The one on the right has higher grade, but a 35 mm coin is very impressive in hand and in that way is better than the one on the right. If you saw them in individual photos like dealers use, their sizes would not be evident. Since the time span for this one type was 50 years, you can imagine that inflation might require making a smaller coin for the same nominal denomination. I think the one on the left is from earlier in that time period than the one on the right. Show us some examples where the size of the coin might not be clear from a photo.