I'm just over 6'1" (so around 186cm) and I ride a 21" hardtail, a 54cm rigid, and an 18" full suspension bike. With the hardtail, I got the 21" because the 19" felt too small but that was just me and my fit on a few different bike brands. You can do calculations all you want but unless you ride these bikes in a couple of different sizes, you'll never know what you need.