Generally, you new fins should fit you in the same way your regular walking shoes should fit your feet. Your fins should have a snug fit on your feet. Just like hiking shoes, a fit that’s too loose will result in uncomfortable chafing and even blisters. At worst, your fins may even slip off while swimming
though this may sound like a crazy idea and counter intuitive, wear socks might be necessary when wearing fins. Some people may wear fins and it fits but they may suffer having blisters or rashes from wearing their fins.
If you get blisters from wearing fins, you may want to consider wearing a pair of either regular athletic socks or specialty “fin socks.
to find out your size for the fin, you can start off with your shoe sizes. a good recommendation is always use open heel fins, and the heel strap can be tightened or loosened a notch during a dive if they are not feeling right without messing up your dive
. Once you get them set to the right size you can leave them in that position and just clip or unclip the strap.