It is going to depend on either your waist size is, or how tall/heavy you are. Find out that stuff and buying the right diaper size shouldn't be much of a problem :smile1:
NICE CALL, man you are all over that great decision stuff!
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Like others have said, package sizes explain everything. So if you are too scared to look at the packages in stores, find them online-- you can get information for literally anything online, and yes that includes waist size measurements for just about every diaper.
As for getting diapers without your parents finding out, that is where the wiki comes into play, because everyone asks the same damn questions it seems.