The present paper deals with analysis of dimensional error in honing and proposes a new automatic sizing system. Thermal deformation of the ring-gauges in calibration, thermal and elastic deformations of the workpiece and the honing head are the causes of dimensional error in honing. An automatic sizing system with a new calibration method and in-process compensation of the thermal and elastic deformations is proposed in order to improve the dimensional accuracy at 20-degrees-C of workpiece. Experimental results obtained under various honing conditions show the validity of the proposed method.