I'm probably not the best person to answer that, I always buy the extended calf version of J.Crew boots and those fit my 15" calf perfectly. I'm not sure what the measurement is on the regular calf, but if you call J.Crew they can tell you the exact measurement.
I always order extended calf as well, and they do vary amongst styles. I have a Melrose (pointy toe kitten heel) from F/W 05/06 that fits my 16.5" calves perfectly, but I also ordered a pair of fab riding boots last winter that didn't fit my right leg at all. I cried for a week afterward.
I would call J. Crew and ask for measurements. Their phone CS is usually helpful, and always nice.