Converting file size in bytes to human-readable string

Question

I m using this function to convert a file size in bytes to a human-readable file size   function getReadableFileSizeString fileSizeInBytes        var i   -1      var byteUnits      kB     MB     GB     TB    PB    EB    ZB    YB        do           fileSizeInBytes   fileSizeInBytes   1024          i          while  fileSizeInBytes  gt  1024        return Math max fileSizeInBytes  0 1  toFixed 1    byteUnits i        However  it seems like this isn t 100  accurate  For example   getReadableFileSizeString 1551859712      output is  1 4 GB    Shouldn t this be  1 5 GB   It seems like the division by 1024 is losing precision  Am I totally misunderstanding something or is there a better way to do this

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Solution as ReactJS Component  Bytes   React createClass       formatBytes             var i   Math floor Math log this props bytes    Math log 1024            return  this props bytes  amp  amp   0 Bytes      this props bytes   Math pow 1024  i   toFixed 2            Bytes    KB    MB    GB    TB    PB    EB    ZB    YB   i             render              return                lt span gt   this formatBytes     lt  span gt                         UPDATE For those using es6 here is a stateless version of this same component  const sufixes     Bytes    KB    MB    GB    TB    PB    EB    ZB    YB    const getBytes    bytes    gt      const i   Math floor Math log bytes    Math log 1024      return  bytes  amp  amp   0 Bytes      bytes   Math pow 1024  i   toFixed 2          sufixes i       const Bytes      bytes      gt    lt span gt   getBytes bytes    lt  span gt     Bytes propTypes       bytes  React PropTypes number

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let bytes   1024   10   10   10   console log getReadableFileSizeString bytes    will return 1000 0   instead of 1MB

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Here is a prototype to convert a number to a readable string respecting the new international standards      There are two ways to represent big numbers  You could either display   them in multiples of 1000   10 3  base 10  or 1024   2 10  base 2   If   you divide by 1000  you probably use the SI prefix names  if you   divide by 1024  you probably use the IEC prefix names  The problem   starts with dividing by 1024  Many applications use the SI prefix   names for it and some use the IEC prefix names  The current situation   is a mess  If you see SI prefix names you do not know whether the   number is divided by 1000 or 1024   https   wiki ubuntu com UnitsPolicy  http   en wikipedia org wiki Template Quantities of bytes  Object defineProperty Number prototype  fileSize   value function a b c d    return  a a  1e3  k   B    1024  K   iB   b Math c b log   d c this  c a 0   0 this b pow a 0  d   toFixed 2         d  a 1   MGTPEZY   --d  a 2   Bytes      writable false enumerable false      This function contains no loop  and so it s probably faster than some other functions   Usage   IEC prefix  console log  186457865  fileSize        default IEC  power 1024    177 82 MiB   KiB MiB GiB TiB PiB EiB ZiB YiB   SI prefix  console log  186457865  fileSize 1      1 true for SI  power 1000    186 46 MB    kB MB GB TB PB EB ZB YB   i set the IEC as default because i always used binary mode to calculate the size of a file    using the power of 1024    If you just want one of them in a short oneliner function   SI  function fileSizeSI a b c d e    return  b Math c b log d 1e3 e c a  c d  0 a b pow d e   toFixed 2         e  kMGTPEZY  --e   B   Bytes       kB MB GB TB PB EB ZB YB   IEC  function fileSizeIEC a b c d e    return  b Math c b log d 1024 e c a  c d  0 a b pow d e   toFixed 2         e  KMGTPEZY  --e   iB   Bytes       KiB MiB GiB TiB PiB EiB ZiB YiB   Usage   console log fileSizeIEC 7412834521      if you have some questions about the functions just ask

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Based on cocco s idea  here s a less compact -but hopefully more comprehensive- example    lt  DOCTYPE html gt   lt html gt   lt head gt   lt title gt File info lt  title gt    lt script gt   lt  -- function fileSize bytes        var exp   Math log bytes    Math log 1024    0      var result    bytes   Math pow 1024  exp   toFixed 2        return result          exp    0    bytes    KMGTPEZY  exp - 1     B       function info input        input nextElementSibling textContent   fileSize input files 0  size      -- gt   lt  script gt   lt  head gt    lt body gt   lt label for  upload-file  gt  File   lt  label gt   lt input id  upload-file  type  file  onchange  info this   gt   lt div gt  lt  div gt   lt  body gt   lt  html gt

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sizeOf   function  bytes      if  bytes    0    return  0 00 B       var e   Math floor Math log bytes    Math log 1024      return  bytes Math pow 1024  e   toFixed 2        KMGTP  charAt e   B          sizeOf 2054110009           1 91 GB         sizeOf 7054110           6 73 MB       sizeOf   3 1024 1024             3 00 MB

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Another example similar to those here  function fileSize b        var u   0  s 1024      while  b  gt   s    -b  gt   s            b    s          u              return  u   b toFixed 1          b      KMGTPEZY  u     B       It measures negligibly better performance than the others with similar features

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Another embodiment of the calculation  function humanFileSize size        var i   Math floor  Math log size    Math log 1024         return   size   Math pow 1024  i    toFixed 2    1           B    kB    MB    GB    TB   i

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A simple and short  quot Pretty Bytes quot  function for the SI system without the unnecessary fractionals rounding  In fact  because the number size is supposed to be human-readable  a  quot 1 of a thousand fraction quot  display is no longer human  The number of decimal places is defaulted to 2 but can be modified on calling the function to other values  The common mostly display is the default 2 decimal place  The code is short and uses the method of Number String Triplets  Hope it is useful and a good addition to the other excellent codes already posted here   x000D   x000D     Simple Pretty Bytes with SI system    Without fraction rounding  function numberPrettyBytesSI Num 0  dec 2   if  Num lt 1000  return Num   Bytes   Num    0  repeat  Num      length 2 3  Num  match    3  g   return Number Num 0       Num 1  substring 0 dec         kMGTPEZY  Num length   B      console log numberPrettyBytesSI 0    console log numberPrettyBytesSI 500    console log numberPrettyBytesSI 1000    console log numberPrettyBytesSI 15000    console log numberPrettyBytesSI 12345    console log numberPrettyBytesSI 123456    console log numberPrettyBytesSI 1234567    console log numberPrettyBytesSI 12345678    x000D   x000D   x000D

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As of 2020  you can use file-size npm package  that supports formatting in  IEC  power 1024  default   SI  power 1000   and JEDEC  Alternative SI Unit Notation   npm install file-size  import filesize from  quot filesize quot       outputs  186 46 MB filesize 186457865  human  si        outputs  177 82 MiB filesize 186457865  human     https   www npmjs com package file-size

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Here s one I wrote   x000D   x000D         Format bytes as human-readable text          param bytes Number of bytes      param si True to use metric  SI  units  aka powers of 1000  False to use               binary  IEC   aka powers of 1024      param dp Number of decimal places to display          return Formatted string      function humanFileSize bytes  si false  dp 1      const thresh   si   1000   1024     if  Math abs bytes   lt  thresh        return bytes     B          const units   si          kB    MB    GB    TB    PB    EB    ZB    YB            KiB    MiB    GiB    TiB    PiB    EiB    ZiB    YiB      let u   -1    const r   10  dp     do       bytes    thresh        u      while  Math round Math abs bytes    r    r  gt   thresh  amp  amp  u  lt  units length - 1       return bytes toFixed dp          units u       console log humanFileSize 1551859712       1 4 GiB console log humanFileSize 5000  true       5 0 kB console log humanFileSize 5000  false       4 9 KiB console log humanFileSize -10000000000000000000000000000       -8271 8 YiB console log humanFileSize 999949  true       999 9 kB console log humanFileSize 999950  true       1 0 MB console log humanFileSize 999950  true  2       999 95 kB console log humanFileSize 999500  true  0       1 MB x000D   x000D   x000D

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It depends on whether you want to use the binary or decimal convention   RAM  for instance  is always measured in binary  so to express 1551859712 as  1 4GiB would be correct   On the other hand  hard disk manufacturers like to use decimal  so they would call it  1 6GB   And just to be confusing  floppy disks use a mixture of the two systems - their 1MB is actually 1024000 bytes

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I found  cocco s answer interesting  but had the following issues with it     Don t modify native types or types you don t own Write clean  readable code for humans  let minifiers optimize code for machines  Bonus for TypeScript users  Doesn t play well with TypeScript   TypeScript           Describes manner by which a quantity of bytes will be formatted      enum ByteFormat              Use Base 10  1 kB   1000 bytes   Recommended for sizes of files on disk  disk sizes  bandwidth          SI   0             Use Base 2  1 KiB   1024 bytes   Recommended for RAM size  size of files on disk          IEC   1           Returns a human-readable representation of a quantity of bytes in the most reasonable unit of magnitude      example    formatBytes 0     returns  0 bytes     formatBytes 1     returns  1 byte     formatBytes 1024  ByteFormat IEC     returns  1 KiB     formatBytes 1024  ByteFormat SI     returns  1 02 kB      param size The size in bytes      param format Format using SI  Base 10  or IEC  Base 2   Defaults to SI      returns A string describing the bytes in the most reasonable unit of magnitude      function formatBytes    value  number    format  ByteFormat   ByteFormat SI       const  multiple  k  suffix     format     ByteFormat SI        1000   k    B          1024   K    iB    as  number  string  string       tslint disable-next-line  no-bitwise   const exp    Math log value    Math log multiple     0      or  if you d prefer not to use bitwise expressions or disabling tslint rules  remove the line above and use the following       const exp   value     0   0   Math floor Math log value    Math log multiple      const size   Number  value   Math pow multiple  exp   toFixed 2     return       size                  exp            k    MGTPEZY   exp - 1    suffix            byte     size     1    s                   example  0  1  1024  Math pow 1024  2   Math floor Math pow 1024  2    2 34   Math pow 1024  3   Math floor Math pow 1024  3    892 2   forEach size   gt      console log  Bytes      size    console log  SI size      formatBytes size     console log  IEC size      formatBytes size  1      n

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Here s mine - works for really big files too - -  function formatFileSize size        var sizes      Bytes     KB     MB     GB     TB     PB     EB     ZB     YB        for  var i   1  i  lt  sizes length  i                  if  size  lt  Math pow 1024  i   return  Math round  size Math pow 1024  i-1   100  100    sizes i-1             return size

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1551859712   1024   1515488 1515488   1024   1479 96875 1479 96875   1024   1 44528198242188   Your solution is correct  The important thing to realize is that in order to get from 1551859712 to 1 5  you have to do divisions by 1000  but bytes are counted in binary-to-decimal chunks of 1024  hence why the Gigabyte value is less

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For those who use Angular  there s a package called angular-pipes that has a pipe for this   File  import   BytesPipe   from  angular-pipes     Usage     150   bytes     lt  -- 150 B -- gt     1024   bytes     lt  -- 1 KB -- gt     1048576   bytes     lt  -- 1 MB -- gt     1024   bytes  0    KB      lt  -- 1 MB -- gt     1073741824   bytes     lt  -- 1 GB -- gt     1099511627776   bytes     lt  -- 1 TB -- gt     1073741824   bytes   0    B     MB      lt  -- 1024 MB -- gt    Link to the docs

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My answer might be late  but I guess it will help someone  Metric prefix         Format file size in metric prefix     param fileSize     returns  string      const formatFileSizeMetric    fileSize    gt      let size   Math abs fileSize      if  Number isNaN size         return  Invalid file size          if  size     0        return  0 bytes          const units     bytes    kB    MB    GB    TB      let quotient   Math floor Math log10 size    3     quotient   quotient  lt  units length   quotient   units length - 1    size     1000    quotient      return     size toFixed 2     units quotient         Binary prefix         Format file size in binary prefix     param fileSize     returns  string      const formatFileSizeBinary    fileSize    gt      let size   Math abs fileSize      if  Number isNaN size         return  Invalid file size          if  size     0        return  0 bytes          const units     bytes    kiB    MiB    GiB    TiB      let quotient   Math floor Math log2 size    10     quotient   quotient  lt  units length   quotient   units length - 1    size     1024    quotient      return     size toFixed 2     units quotient         Examples     Metrics prefix formatFileSizeMetric 0          0 bytes formatFileSizeMetric -1         1 bytes formatFileSizeMetric 100        100 bytes formatFileSizeMetric 1000       1 kB formatFileSizeMetric 10  5      10 kB formatFileSizeMetric 10  6      1 MB formatFileSizeMetric 10  9      1GB formatFileSizeMetric 10  12     1 TB formatFileSizeMetric 10  15     1000 TB     Binary prefix formatFileSizeBinary 0         0 bytes formatFileSizeBinary -1        1 bytes formatFileSizeBinary 1024      1 kiB formatFileSizeBinary 2048      2 kiB formatFileSizeBinary 2  20     1 MiB formatFileSizeBinary 2  30     1 GiB formatFileSizeBinary 2  40     1 TiB formatFileSizeBinary 2  50     1024 TiB

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This is size improvement of mpen answer  function humanFileSize bytes  si false      let u  b bytes  t  si   1000   1024              si  k   K       MGTPEZY   find x  gt   u x  b  t  b  2 lt 1      return    u    t b  toFixed 1    bytes    u    si  amp  amp  u    i     B            x000D   x000D  function humanFileSize bytes  si false    x000D    let u  b bytes  t  si   1000   1024       x000D         si  k   K       MGTPEZY   find x  gt   u x  b  t  b  2 lt 1    x000D    return    u    t b  toFixed 1    bytes    u    si  amp  amp  u    i     B       x000D    x000D   x000D   x000D     TEST x000D  console log humanFileSize 5000            4 9 KiB x000D  console log humanFileSize 5000 true       5 0 kB x000D   x000D   x000D

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There are lots of great answers here  But if your looking for a really simple way  and you don t mind a popular library  a great solution is filesize  https   www npmjs com package filesize It has lots of options and the usage is simple e g  filesize 265318       quot 259 1 KB quot   Taken from their excellent examples

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Based on cocco s answer but slightly desugerified  honestly  ones I was comfortable with are remained added  and doesn t show trailing zeros but still supports 0  hope to be useful for others    x000D   x000D  function fileSizeSI size    x000D      var e    Math log size    Math log 1e3     0  x000D      return   size   Math pow 1e3  e   toFixed 2            kMGTPEZY  e - 1            B   x000D    x000D   x000D   x000D     test  x000D  document write  0  23  4322  324232132  22e9  64 22e12  76 22e15  64 66e18  77 11e21  22e24  map fileSizeSI  join   lt br gt      x000D   x000D   x000D

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I wanted the  file manager  behavior  e g   Windows Explorer  where the number of decimal places is proportional to the number size  Seemingly none of the other answers does this   function humanFileSize size        if  size  lt  1024  return size     B      let i   Math floor Math log size    Math log 1024       let num    size   Math pow 1024  i       let round   Math round num      num   round  lt  10   num toFixed 2    round  lt  100   num toFixed 1    round     return    num     KMGTPEZY  i-1  B      Here s some examples   humanFileSize 0               0 B  humanFileSize 1023            1023 B  humanFileSize 1024            1 00 KB  humanFileSize 10240           10 0 KB  humanFileSize 102400          100 KB  humanFileSize 1024000         1000 KB  humanFileSize 12345678        11 8 MB  humanFileSize 1234567890      1 15 GB

[javascript] Converting file size in bytes to human-readable string

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