Thanks, Mark - the sellor claimed it was a 56cm (same as the red M2). It fits more like a 57-58cm and with the stack of spacers, it rides much higher than all my others. I use this one for rough weather and also on the trainer in the basement (more upright riding position for "spinning"). In fact, it is covered in 1/2" of salt, sand, and grit from earlier today. Nasty...

I can't complain - the frame was only $46 three years ago...under $300 for the whole build.