>>1318044It actually doesn't vary that much across brands, especially when it comes to older bikes. They are measured from the center of the crank to the top of the seat tube.
I am 6'4" with a 34 inch inseam. I rider a 61-64 cm frame. All I have to do is measure a seatube from C to T and I know if it will fit me. For modern bikes with a sloping top tube it is a little different. I still ride the same size frame but the C to T will be shorter. My 61cm lemond has a C to T of 585mm but is a "virtual 61" with whatever bullshit the sloping geometry uses, I think it is top tube length.
