Inseam is the most important thing.
I'm 5/10 with long legs, so a 56 is about right for
me.
Another problem is that different manufacturers
measure their frames differently. Some to the center
of the tubes, some to the top, of the seat tube, etc.
If you raise the seat about halfway to the mark on the
seat post that says "maximum height", then get on
the bike, and have (almost) full leg extension on the
downmost part of the crank swing, then the bike
should work for you. There are other factors involved,
like how far forward the handlebar post causes
you to ride, but that can be adjusted with a different
handlebar bracket.
If you can bring the thing to a bike shop, they can
give you a quick assessment on whether the bike
fits you.