How long did Qin Shi Huang rule China?

According to the historical book Shiji (史记), Qin Shi-huang (秦始皇) whose name is Ying Zheng (嬴政) born in the 1st month 48th year during the reign of Qin Zhao-xiang-wang (秦昭襄王), the his great-grandfather. Thus, the birthday of Qin Shi-huang is reckoned to be 19th October, 259 BC.