I never had to go half size up with Yonex but others say they do. I personally think you must try for yourself, get a model thats suited to your foot shape too. Comfort Z2/Aerus 3 is good for normal-narrow feet. 65ZM2 good for normal feet. And apparently Eclipsion Z and 03ZM good for normal-wide feet. This is the general impressions from this forum. I've tried comfort z2, 65zm2 and Aerus 3 myself if you have any questions about those models just ask.