| Bits per second (bit/s) | Yobibits per second (Yibit/s) |
|---|---|
| 1 Bit per second | 8.27180612553 × 10-25 Yibit/s |
| 2 Bits per second | 1.65436122511 × 10-24 Yibit/s |
| 3 Bits per second | 2.48154183766 × 10-24 Yibit/s |
| 4 Bits per second | 3.30872245021 × 10-24 Yibit/s |
| 5 Bits per second | 4.13590306277 × 10-24 Yibit/s |
| 10 Bits per second | 8.27180612553 × 10-24 Yibit/s |
| 20 Bits per second | 1.65436122511 × 10-23 Yibit/s |
| 25 Bits per second | 2.06795153138 × 10-23 Yibit/s |
| 50 Bits per second | 4.13590306277 × 10-23 Yibit/s |
| 100 Bits per second | 8.27180612553 × 10-23 Yibit/s |
| Reference | Bits per second (bit/s) | Yobibits per second (Yibit/s) |
|---|---|---|
| A dial-up modem | 56000 bit/s | 4.63221 × 10-20 Yibit/s |
| Typical home broadband | 100000000 bit/s | 8.27181 × 10-17 Yibit/s |
| Gigabit Ethernet | 1 × 109 bit/s | 8.27181 × 10-16 Yibit/s |
| Streaming a 4K film | 25000000 bit/s | 2.06795 × 10-17 Yibit/s |
The bit per second is the fundamental unit of data transfer rate. Its symbol is bit/s, often written bps. It counts how many binary decisions a channel carries in one second, and every other unit of transmission speed is a multiple of it.
Because it is a rate, it has the form of a quantity divided by time, exactly like metres per second or litres per second. That makes the arithmetic straightforward: a link running at a given number of bits per second, multiplied by a duration in seconds, gives the total number of bits transferred, and dividing by eight converts that to octets.
The unit must be distinguished from the baud, which counts symbols per second rather than bits. Early modems transmitted one bit per symbol, so the two numbers were the same and the words were used interchangeably. Modern schemes encode several bits in each symbol — by varying phase and amplitude together — so a channel running at 3,000 baud may carry 33,600 bits per second. Only the bit rate describes how much information moves.
Claude Shannon established the theoretical ceiling in 1948. The capacity of a channel in bits per second depends on its bandwidth and on the ratio of signal to noise, and no coding scheme can exceed it. Every advance in modem and radio design since has been an attempt to approach that limit more closely, and modern systems come within a fraction of a decibel of it.
In practice the raw bit rate of a link is never the rate at which useful data arrives. Protocol headers, error-correcting codes, acknowledgements and retransmissions all consume capacity, and the usable fraction is typically 90 to 95 per cent on a wired link and considerably less on a shared wireless one.
Single bits per second are rarely quoted, because almost every channel is faster. The exceptions are deep-space communication, where a probe billions of kilometres away may return data at a few tens of bits per second, and certain low-power sensor networks that transmit a handful of bits at long intervals to preserve battery life.
One bit per second equals 0.125 octets per second, 0.001 kilobits per second, or about 0.0009766 kibibits per second.
The yobibit per second is a unit of data transfer rate equal to two to the eightieth power bits per second, which is 1,024 zebibits per second. Its symbol is Yibit/s. It is the largest binary transfer rate the International Electrotechnical Commission has named, and the binary counterpart of the yottabit per second.
At this final step the binary and decimal conventions differ by 20.9 per cent, and that number is the conclusion of the argument the IEC prefixes were created to settle. A naming habit that was 2.4 per cent wrong at the kibibit has grown, through eight successive multiplications by 1.024, into a discrepancy of more than a fifth. No measurement system can carry an ambiguity that large.
The unit describes nothing. Global internet traffic runs at roughly an exabit per second, so a yobibit per second is over a million times the total communication of the human species. No link, no aggregate and no forecast reaches it, and none is expected to.
The binary series stops here because the decimal series stopped at yotta when the IEC standard was written in 1998. When ronna and quetta were added to the metric system in 2022, no matching binary names were defined, so a rate of two to the ninetieth bits per second has no accepted short form. That gap will presumably be filled if it is ever needed, which at present it is not.
Defining a rung of a ladder nobody has climbed still has a purpose. A system whose names run out forces its users to improvise, and improvised extensions conflict; writing the whole series out in advance means the rule, rather than a table of exceptions, is all anyone has to learn. That is the same reasoning that gave the metric system its complete prefix set.
For any reader of technical material the lesson of the whole binary series is a single character. Kibit/s, Mibit/s, Gibit/s, Tibit/s, Pibit/s, Eibit/s, Zibit/s and Yibit/s are binary; kbit/s, Mbit/s, Gbit/s, Tbit/s, Pbit/s, Ebit/s, Zbit/s and Ybit/s are decimal; and the difference between them widens from a rounding error to a fifth as you climb.
One yobibit per second equals 1,024 zebibits per second, 151,115,727,451,828,646,838,272 octets per second, or about 1.209 yottabits per second.