A kilobyte is 103 or 1,000 bytes.
The kilobyte (abbreviated "K" or "KB") is the smallest unit of measurement greater than a byte. It precedes the megabyte, which contains 1,000,000 bytes. While one kilobyte is technically 1,000 bytes, kilobytes are often used synonymously with kibibytes, which contain 1,024 bytes.
Kilobytes are most often used to measure the size of small files. For example, a plain text document may contain 10 KB of data and therefore would have a file size of 10 kilobytes. Small website graphics are often between 5 KB and 100 KB in size. While some files contain less than 4 KB of data, modern file systems such as NTFS (Windows) and HFS+ (Mac) have a cluster size of 4 KB. Therefore, individual files typically take up a minimum of four kilobytes of disk space.
NOTE: For a list of other units of measurement, view this Help Center article.