To address the topic of this thread, I have found that sizes vary by manufacturer, and even then they may vary by suit model. And you cannot just go by the numbers, either.
For example, the Nike Men's Performance swimwear comes in sizes 28, 30, 32, 34 and so on. You would guess that number is the waist size in inches. But it isn't. According to the
official size chart, their size 30 actually fits waist sizes 31-33! (I was very pleased to find that my perfect size was 34 -- I have not worn size 34 in ages! Ha ha!)
So, I suggest you always consult size charts.. but then they can be deceiving, as well, so, if I am shopping online-- I always check the reviews of the suit I am after to see if other buyers felt the sizing was right on or too small or too big.
Another thing I did was I went to a local sporting goods store to try on the brand I was looking to buy online to see if I could get a good feel for the fit of the suit. But, again, if it is not the exact model you are looking to buy online, beware that the sizing may still be a little off. Also suits of nylon Spandex usually have more give, and will stretch bigger, as opposed to polyester/PBT suits.
Just some advice that I hope helps.