I read the reviews about this fin running small so I bought a 4/5 (size7.5) but it was too small. Send back and got the next size up. It fits fine but needs getting broke in before long distance swimming. I preferred another aquasphere fin with split fins but I went through 2 pairs in a year, they split.  Perhaps they are no longer on the market because I didn't see them when i ordered these. One these get broke in i might want to change to a 4star

The fins work great. They don't rub and are not uncomfortable in any way. I ordered a size that sounds ridiculously small (2-3), but I wear a woman's size 5 1/2 shoe and they fit perfectly.

I went with my shoe size. Jump in the water, slip them on like slippers, do your swim kick. The first thing you notice is you are passing the other lap swimmers! After an hour workout my feet a little chafing on the knuckles. No pain, no gain.

Great fin.  The sizes are in men's.  I wear size 7 women's shoe & fit beautifully in to fin size 4-5.
Practical and good work out fins for daily swim exercise, workout or water aerobic use.

I take size 7 to 7.5 shoe so I order the 6-7. Way too big. Returned for 1 size down and fit perfectly. Good workout wearing the fins.

I glide right through the water with these.  Great leg work out.  I wear a women's size 8 and ordered a 5/6. Fits perfectly.