8wks measurements for a fetus is 1/2 in right? if so why did doc say i'm 8 w when fetus measures 1.7in?

Measurement in cm?: You're right, expected length of an 8w fetus is roughly 0.6in. This is about 1.6cm. Wonder if this is just a matter of using different units to describe the same thing.

Conversion confusion: As you say, an 8 week fetus should measure ~1/2 inch from crown-to rump (distance from the top of the skull to the base of the spine). However, your obstetrician is conveying the fetus's crown-to-rump length in centimeters. 1/2 inch is ABOUT 1.7 centimeters, consistent with a gestational age of 8 weeks. I hope this clears up the confusion.