units(7) - man - phpman

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⚡ TLDR: units (tldr-pages)

Convert between two units of measure.

Run in interactive mode
units
List all units containing a specific string in interactive mode
search {{string}}
Show the conversion between two simple units
units {{quarts}} {{tablespoons}}
Convert between units with quantities
units "{{15 pounds}}" {{kilograms}}
Show the conversion between two compound units
units "{{meters / second}}" "{{inches / hour}}"
Show the conversion between units with different dimensions
units "{{acres}}" "{{ft^2}}"
Show the conversion of byte multipliers
units "{{15 megabytes}}" {{bytes}}

UNITS(7)                              Linux Programmer's Manual                             UNITS(7)



NAME
       units - decimal and binary prefixes

DESCRIPTION
   Decimal prefixes
       The SI system of units uses prefixes that indicate powers of ten.  A kilometer is 1000 meter,
       and a megawatt is 1000000 watt.  Below the standard prefixes.

              Prefix   Name    Value
              y        yocto   10^-24 = 0.000000000000000000000001
              z        zepto   10^-21 = 0.000000000000000000001
              a        atto    10^-18 = 0.000000000000000001
              f        femto   10^-15 = 0.000000000000001
              p        pico    10^-12 = 0.000000000001
              n        nano    10^-9  = 0.000000001
              µ        micro   10^-6  = 0.000001
              m        milli   10^-3  = 0.001
              c        centi   10^-2  = 0.01
              d        deci    10^-1  = 0.1
              da       deka    10^ 1  = 10
              h        hecto   10^ 2  = 100
              k        kilo    10^ 3  = 1000
              M        mega    10^ 6  = 1000000
              G        giga    10^ 9  = 1000000000
              T        tera    10^12  = 1000000000000
              P        peta    10^15  = 1000000000000000
              E        exa     10^18  = 1000000000000000000
              Z        zetta   10^21  = 1000000000000000000000
              Y        yotta   10^24  = 1000000000000000000000000

       The symbol for micro is the Greek letter mu, often written u in an ASCII context  where  this
       Greek letter is not available.  See also

              ⟨http://physics.nist.gov/cuu/Units/prefixes.html⟩

   Binary prefixes
       The  binary  prefixes  resemble the decimal ones, but have an additional 'i' (and "Ki" starts
       with a capital 'K').  The names are formed by taking the first syllable of the names  of  the
       decimal prefix with roughly the same size, followed by "bi" for "binary".

              Prefix   Name   Value
              Ki       kibi   2^10 = 1024
              Mi       mebi   2^20 = 1048576
              Gi       gibi   2^30 = 1073741824
              Ti       tebi   2^40 = 1099511627776
              Pi       pebi   2^50 = 1125899906842624
              Ei       exbi   2^60 = 1152921504606846976

       See also

       ⟨http://physics.nist.gov/cuu/Units/binary.html⟩

   Discussion
       Before  these binary prefixes were introduced, it was fairly common to use k=1000 and K=1024,
       just like b=bit, B=byte.  Unfortunately, the M is capital already, and cannot be  capitalized
       to indicate binary-ness.

       At  first that didn't matter too much, since memory modules and disks came in sizes that were
       powers of two, so everyone knew that in such contexts "kilobyte" and  "megabyte"  meant  1024
       and 1048576 bytes, respectively.  What originally was a sloppy use of the prefixes "kilo" and
       "mega" started to become regarded as the "real true meaning" when  computers  were  involved.
       But then disk technology changed, and disk sizes became arbitrary numbers.  After a period of
       uncertainty all  disk  manufacturers  settled  on  the  standard,  namely  k=1000,  M=1000 k,
       G=1000 M.

       The situation was messy: in the 14k4 modems, k=1000; in the 1.44 MB diskettes, M=1024000; and
       so on.  In 1998 the IEC approved the standard that defines the binary prefixes  given  above,
       enabling people to be precise and unambiguous.

       Thus, today, MB = 1000000 B and MiB = 1048576 B.

       In the free software world programs are slowly being changed to conform.  When the Linux ker‐
       nel boots and says

           hda: 120064896 sectors (61473 MB) w/2048KiB Cache

       the MB are megabytes and the KiB are kibibytes.

COLOPHON
       This page is part of release 5.10 of the Linux  man-pages  project.   A  description  of  the
       project,  information about reporting bugs, and the latest version of this page, can be found
       at https://www.kernel.org/doc/man-pages/.



Linux                                        2020-08-13                                     UNITS(7)