16.5 cm/6.5 inches. It’s definitely wearable, it just feels a little oversized like a flieger is supposed to. I usually prefer 35mm watches, so I’m probably biased towards smaller watches though. I’m just writing it since I sometimes see people getting smaller fliegers and expect them to fit like field watches, and I feel the two types feel quite different regardless of size. Another thing to consider is that the dial is not really black, but more dark greyish. Mine came on a black rubber strap, and I didn’t like how that looked with the dial. Despite the Stowa case looking modern, the watch will always feel a little vintage due to the grey dial and yellow lume. I wanted this watch for several years, but I’m not wearing it that much after finally getting it.
You could get away with it because of the size, but I don’t think it’s any more dressy than say a Casio A158. It’s more stylised and minimalist than dressy. I consider something like a Calatrava with dauphine hands and polished indices a true dress watch. Even something in the Datejust/Oyster Perpetual style looks more dressy to me than this. People frequently wear sports watches with suits, so anything goes, but I wouldn’t get this for the sole purpose of using it as a dress watch.