千字节（kilobyte），常写作kB或K，是一种信息计量单位，现今通常在标示内存等具有一般容量的储存媒介之储存容量时使用。

由于混淆已经普遍化，所以Megabyte往往指Mebibyte，其换算是：

The kilobyte is a multiple of the unit byte for digital information. The International System of Units (SI) defines the prefix kilo as 1000 (10); therefore one kilobyte is 1000 bytes. The unit symbol for the kilobyte is kB. In some fields of information technology kilobyte has traditionally also been used to denote 1024 (2) bytes, which arises from binary exponentiation common to digital circuitry. In this context the unit symbol K or KB has been common.