1units(7) Miscellaneous Information Manual units(7)
2
6 units - decimal and binary prefixes
7
9 Decimal prefixes
10 The SI system of units uses prefixes that indicate powers of ten. A
11 kilometer is 1000 meter, and a megawatt is 1000000 watt. Below the
12 standard prefixes.
13 Prefix Name Value
15 q quecto 10^-30 = 0.000000000000000000000000000001
16 r ronto 10^-27 = 0.000000000000000000000000001
17 y yocto 10^-24 = 0.000000000000000000000001
18 z zepto 10^-21 = 0.000000000000000000001
19 a atto 10^-18 = 0.000000000000000001
20 f femto 10^-15 = 0.000000000000001
21 p pico 10^-12 = 0.000000000001
22 n nano 10^-9 = 0.000000001
23 µ micro 10^-6 = 0.000001
24 m milli 10^-3 = 0.001
25 c centi 10^-2 = 0.01
26 d deci 10^-1 = 0.1
27 da deka 10^ 1 = 10
28 h hecto 10^ 2 = 100
29 k kilo 10^ 3 = 1000
30 M mega 10^ 6 = 1000000
31 G giga 10^ 9 = 1000000000
32 T tera 10^12 = 1000000000000
33 P peta 10^15 = 1000000000000000
34 E exa 10^18 = 1000000000000000000
35 Z zetta 10^21 = 1000000000000000000000
36 Y yotta 10^24 = 1000000000000000000000000
37 R ronna 10^27 = 1000000000000000000000000000
38 Q quetta 10^30 = 1000000000000000000000000000000
39 The symbol for micro is the Greek letter mu, often written u in an
41 ASCII context where this Greek letter is not available.
42 Binary prefixes
44 The binary prefixes resemble the decimal ones, but have an additional
45 'i' (and "Ki" starts with a capital 'K'). The names are formed by tak‐
46 ing the first syllable of the names of the decimal prefix with roughly
47 the same size, followed by "bi" for "binary".
48 Prefix Name Value
50 Ki kibi 2^10 = 1024
51 Mi mebi 2^20 = 1048576
52 Gi gibi 2^30 = 1073741824
53 Ti tebi 2^40 = 1099511627776
54 Pi pebi 2^50 = 1125899906842624
55 Ei exbi 2^60 = 1152921504606846976
56 Zi zebi 2^70 = 1180591620717411303424
57 Yi yobi 2^80 = 1208925819614629174706176
58 Discussion
60 Before these binary prefixes were introduced, it was fairly common to
61 use k=1000 and K=1024, just like b=bit, B=byte. Unfortunately, the M
62 is capital already, and cannot be capitalized to indicate binary-ness.
63 At first that didn't matter too much, since memory modules and disks
65 came in sizes that were powers of two, so everyone knew that in such
66 contexts "kilobyte" and "megabyte" meant 1024 and 1048576 bytes, re‐
67 spectively. What originally was a sloppy use of the prefixes "kilo"
68 and "mega" started to become regarded as the "real true meaning" when
69 computers were involved. But then disk technology changed, and disk
70 sizes became arbitrary numbers. After a period of uncertainty all disk
71 manufacturers settled on the standard, namely k=1000, M=1000 k,
72 G=1000 M.
73 The situation was messy: in the 14k4 modems, k=1000; in the 1.44 MB
75 diskettes, M=1024000; and so on. In 1998 the IEC approved the standard
76 that defines the binary prefixes given above, enabling people to be
77 precise and unambiguous.
78 Thus, today, MB = 1000000 B and MiB = 1048576 B.
80 In the free software world programs are slowly being changed to con‐
82 form. When the Linux kernel boots and says
83 hda: 120064896 sectors (61473 MB) w/2048KiB Cache
85 the MB are megabytes and the KiB are kibibytes.
87
89 The International System of Units ⟨https://www.bipm.org/documents/
90 20126/41483022/SI-Brochure-9.pdf⟩.
91Linux man-pages 6.05 2023-02-10 units(7)