The kilobit per second (kbps, or kbit/s, or kb/s) is a unit of measurement for the speed of data transfer. One kilobit per second is 1,000 bits per second. Other common multipliers follow the metric progression; Mbps (megabits per second), Gbps (gigabits per second), and Tbps (terabits per second).

A bit is the smallest unit of data; it cannot be broken down into smaller units. A bit is either on or off; 0 or 1. For example, seven bits are required to communicate a single ASCII character.

Alternate Usage

Another way to express transfer rates is in bytes per second, which uses the capital B: KBps, MBps, GPBs, and TBps. A byte is 8 bits, so to convert from bits to bytes, divide the number by 8. To convert from bytes to bits, multiply by 8.

Common Examples

Most contemporary modems operate at around 56,000 bits per second, and often cite “56k” as their speed. Digital Subscriber Line (DSL) Internet access available to consumers usually operates between 128 Kbps and 3 Mbps (3,000 Kbps, or 3,000,000 bps.) Broadband speeds for residential uses are often in the megabit range, while Internet Service Providers and commercial entities frequently have Internet or local network connectivity in the gigabit or terabit per second ranges.

Besides networking, another common usage of the bit per second standard is for digital media: speech, music and video. A minimal transfer rate for recognizable human speech is around 4 kbps. Standard telephone quality is 8 kbps. MP3 music files are often encoded between 128 kbps and 192 kbps. High definition video formats such as digital television can use anywhere from 8 to 20 Mbps. High definition Blu-ray can be anywhere from 36 to 54 Mbps.

The History of Transfer Rates

An alternate unit of data transfer used prior to bits per second was the baud. Baud refers to state changes per second. Modems (MOdulator-DEModulator) used to measure their speed in baud. Some of the oldest consumer-available modems communicated over standard analog telephone lines at 300 baud, and also at 300 bits per second. However, as modem technology advanced, compression and other techniques were able to get higher and bit per second transfer rates without a corresponding linear increase in state changes. Baud became an outdated term because it wasn’t able to accurately and proportionately express transfer rates, so bps became the standard.