Need help choosing my chainring and size whilst moving from 3x7 to 1x7
what chainring size would anyone recommend?


We can't answer that directly, as we don't know anything about you or the riding you want to do, however, we can help you figure it out.

Start by riding exclusively in the middle ring. Can you do all the riding you want to do using that chainring? If it feels too low, try riding exclusively in the big ring. If that feels too high pick a new ring size between the two. If the middle ring feels too high do the same experiment with the small ring.

What you may also conclude is that you just don't have enough gear range with a 7 speed cassette and you should stick with the triple crank.