Generate a human friendly, readable file size from a number value.

<?php

/**
 * Takes a humanized value of size.
 *
 * @static
 * @access public
 * @param int $fileSize
 * @param array $options
 * @return string
 * @links http://en.wikipedia.org/wiki/Units_of_information
 */
function humanizeSize($fileSize, $options = array())
{
  isset($options['unit']) || $options['unit'] = 'byte';
  isset($options['standard']) || $options['standard'] = 'si';
  isset($options['width']) || $options['width'] = 'narrow';
  isset($options['prefix']) || $options['prefix'] = ' ';
  isset($options['round']) || $options['round'] = 2;

  $options['units'] = array(
    'byte' => array(
      'singular' => array(
        'narrow' => 'B',
        'wide' => 'byte'
      ),
      'plural' => array(
        'narrow' => 'B',
        'wide' => 'bytes'
      )
    ),
    'bit' => array(
      'singular' => array(
        'narrow' => 'bit',
        'wide' => 'bit'
      ),
      'plural' => array(
        'narrow' => 'bits',
        'wide' => 'bits'
      )
    )
  );

  $options['standards'] = array(
    'si' => array(
      'narrow' => array(
        "",
        "k",
        "M",
        "G",
        "T",
        "P",
        "E",
        "Z",
        "Y"
      ),
      'wide' => array(
        "",
        "kilo",
        "mega",
        "giga",
        "tera",
        "peta",
        "exa",
        "zetta",
        "yotta"
      )
    ),
    'iec' => array(
      'narrow' => array(
        "",
        "Ki",
        "Mi",
        "Gi",
        "Ti",
        "Pi",
        "Ei",
        "Zi",
        "Yi"
      ),
      'wide' => array(
        "",
        "kibi",
        "mebi",
        "gibi",
        "tebi",
        "pebi",
        "exbi",
        "zebi",
        "yobi"
      )
    )
  );

  switch ($options['unit'] = strtolower($options['unit'])) {
    case 'bit':
    case 'bits':
    case 'b':
      $options['unit'] = 'bit';
      break;
    default:
      $options['unit'] = 'byte';
  }

  switch ($options['standard'] = strtolower($options['standard'])) {
    case 'i':
    case 'iec':
      $options['standard'] = 'iec';
      break;
    default:
      $options['standard'] = 'si';
  }

  switch ($options['width'] = strtolower($options['width'])) {
    case 'w':
    case 'wide':
      $options['width'] = 'wide';
      break;
    default:
      $options['width'] = 'narrow';
  }

  $factor = ($options['standard'] == 'si') ? 1000 : 1024;
  $i = 0;
  if ($options['unit'] == 'bit') {
    $fileSize *= 8;
  }

  while ($fileSize > $factor) {
    $fileSize /= $factor;
    $i++;
  }

  $fileSize     = round($fileSize, $options['round']);
  $n            = $fileSize == 0 || $fileSize == 1 ? 'singular' : 'plural';
  $humanizeSize = $fileSize . $options['prefix'] . $options['standards'][$options['standard']][$options['width']][$i] . $options['units'][$options['unit']][$n][$options['width']];

  return $humanizeSize;
}

// example usage
// -------------

$file = 'myisofile.iso';
$file_size_as_bytes = filesize($file);

echo 'File: ' . $file . "n";
echo 'Bytes: ' . $file_size_as_bytes . "n";

$friendly = humanizeSize($file_size_as_bytes);

echo 'Humanized: ' . $friendly;

// output...
// File: myisofile.iso
// Bytes: 637597696
// Humanized: 637.6 MB

?>