Bit rate

In telecommunications and computing, bit rate (bitrate or as a variable R) is the number of bits that are conveyed or processed per unit of time.

The bit rate is expressed as bits per second (symbol: bit/s), often with an SI prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s). The non-standard abbreviation bps is often used: 1 Mbps is 1 Mbit/s, that is, one million bits per second.

The bit rate is different from the transfer rate, measured in transfers per second, when the channel is parallel and thus transfers multiple bits per transfer.

In most computing and digital communication environments, one byte per second (symbol: B/s) corresponds to 8 bit/s (1 byte = 8 bits). However if stop bits, start bits, and parity bits need to be factored in, a higher number of bits per second will be required to achieve a throughput of the same number of bytes.

Prefixes

For large or small bit rates, SI prefixes (also known as metric prefixes or decimal prefixes) are used:

The binary prefixes defined by International Standard IEC 80000-13 are sometimes used: e.g., 1 KiB/s = 1024 B/s = 8192 bit/s, and 1 MiB/s = 1024 KiB/s.

In data communications

Gross bit rate

In digital communication systems, the physical layer gross bitrate, raw bitrate, data signaling rate, gross data transfer rate or uncoded transmission rate (sometimes written as a variable Rb or fb) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.

In case of serial communications, the gross bit rate is related to the bit transmission time

T

b

{\displaystyle T_{\text{b}}}

as:

R

b

=

1

T

b

,

{\displaystyle R_{\text{b}}={1 \over T_{\text{b}}},}

The gross bit rate is related to the symbol rate or modulation rate, which is expressed in baud or symbols per second. However, the gross bit rate and the baud value are equal only when there are only two levels per symbol, representing 0 and 1, meaning that each symbol of a data transmission system carries exactly one bit of data; this is not the case for modern modulation systems used in modems and LAN equipment.