In computer networking and computer science, digital bandwidth or just bandwidth is the capacity for a given system to transfer data over a connection. It is measured as a bit rate expressed in in bits/s or multiples of it (kb/s Mb/s etc.). Digital bandwidth should not be confused with the network throughput, which is the average rate of successful data transfer through a connection. It should also be distinguished from "data transfer", which is the quantity of data transferred over a given period of time.

The maximum bit rate is called "bandwidth" because, according to Hartley's law, the maximum data rate of a physical communication link is related to its bandwidth in hertz, which is sometimes called "analog bandwidth" in computer networking literature. For the case of high signal-to-noise ratio, the digital bandwidth of a bit stream or logical link in a computer network is proportional to the average spectral bandwidth of the analog signal representing the bit stream during a studied time interval.

Some authors prefer terms such as gross bit rate, net bit rate or channel capacity, to avoid confusion between bandwidth in bits per second and analog bandwidth in hertz.

Bandwidth in web hosting

In website hosting, the term "bandwidth" is often used to describe the amount of data transferred to or from the website or server within a prescribed period of time. Another more specific phrase used for this meaning of bandwidth is monthly data transfer.

Web hosting companies often quote a monthly bandwidth limit for a website, for example 500 gigabytes per month. If the total amount of data downloaded from the website in a particular month reaches this limit, the hosting company may shut off further public access to the site.

When a website grows in popularity or exceeds its bandwidth limits, webmasters may reduce bandwidth usage by employing bandwidth optimization techniques.

Internet connection speeds

Below is a table showing the maximum bandwidth of different connection types to the internet: