at 08:32 AM
What are your chest, waist, shoulders, and inseam and weight?
A lot depends on your body proportions. Everyone is different.
For example I'm also 5'7" but I weigh 120 pounds. I have a rather short torso and longer legs. My waist is 28 and hips are 33. Chest size is 32. Shoulders 16.
I wear a 36 in a 618.
The 34 fits me better in the shoulders and chest but it's 23.75" long making it fall at my hips. So it's about an inch too small to close comfortably. So I had to size up. If it were 22" then it would fit me like a glove because the bottom sweep of the size 34 fits someone with a 28 to 30 waist.
Someone with my measurements except 3 or 4" taller would easily fit into a 34.
That's why some guys who are 5'10" and have a 38" chest can also wear a 36 because they have a 32" waist and the jacket hits them at their waist, not at the hips like it does on me.
If you're average sized and not skinny like me you might need a 38 if you want to be able to close the jacket unless you have short legs, a really long torso and/or narrow hips.
Keep in mind that Schott's tend to fit better on average to taller guys who happen have smaller waists. For shorter guys like us, the back length and the bottom sweep of the jacket are much more important indicators of fit rather than the chest size measurement because of where bottom sweep of the jacket falls.
Of course if you're fine with not being able to zip up the jacket then by all means, go with the chest size measurement.
Fortunately, Schott provides for one free exchange. So chances are if you get a jacket that's slightly too small or too big, exchanging for the next size up or down will probably get you the right fit.