code: private function getByteSize($verboseSize)
      {
          if (empty($verboseSize)) {
              return 0;
          }
          if (is_numeric($verboseSize)) {
              return (int) $verboseSize;
          }
          $sizeUnit = trim($verboseSize, '0123456789');
          $size = trim(str_replace($sizeUnit, '', $verboseSize));
          if (!is_numeric($size)) {
              return 0;
          }
          switch (strtolower($sizeUnit)) {
              case 'kb':
              case 'k':
                  return $size * 1024;
              case 'mb':
              case 'm':
                  return $size * 1024 * 1024;
              case 'gb':
              case 'g':
                  return $size * 1024 * 1024 * 1024;
              default:
                  return 0;
          }
      }
docs: Gets the size in bytes from verbose size representation.
  
  For example: '5K' => 5*1024.
  @param string $verboseSize verbose size representation.
  @return int actual size in bytes.