Frame Size-Compact to Road
 

I currently have a Giant FCR Zero compact frame, size 50cm medium, Fits me just fine, at 5ft 11.

I am looking at a Trek 1500 and a Giant TCR Ultrega, in the Trek the shop say 56cm-Because is a Traditional Road frame design, in the Giant they say 53.5cm because it's a semi compact design!

Anyone being here before?

the effective TT size of your M FCR is 54.9, the effecttive TT size of a TCR frame, size M, is 55.4

IIRC treks size differently, and yes a 56 Trek would be a similar size to a M giant TCR

I'm sure a Trek rider could chime in with more concise info.

Giant should have a size chart that compares their frame sizes to "virtual" standard geometry frame sizes. You should also look at top tube length, head tube length, and seat tube angle. Of course, geometry numbers don't matter if you test ride the bike and love the way it fits and handles.