A kilobit is 103 or 1,000 bits.
One kilobit (abbreviated "Kb") contains one thousand bits and there are 1,000 kilobits in a megabit. Kilobits (Kb) are smaller than than kilobytes (KB), since there are 8 kilobits in a single kilobyte. Therefore, a kilobit is one-eighth the size of a kilobyte.
Before broadband Internet was common, Internet connection speeds were often measured in kilobits. For example, a 28.8K modem was able to receive data up to 28.8 kilobits per second (Kbps). A 56K modem could receive data up to 56 Kbps. Most ISPs now offer connection speeds of 10 Mbps and higher, so kilobits are not as commonly used. However, if you download a file from a server that does not have a lot of bandwidth, your system might receive less than 1 Mbps. In this case, the download speed may be displayed in kilobits per second.
NOTE: While kilobits are used to measure data transfer rates, kilobytes are used to measure file size. Therefore, if you download an 800 KB file at 400 Kbps, it will take 16 seconds (rather than 2). This is because 400 kilobits per second is equal to 50 kilobytes per second.
Updated: October 3, 2013