human readable file size

Try something like this:

function humanFileSize($size,$unit="") {
  if( (!$unit && $size >= 1<<30) || $unit == "GB")
    return number_format($size/(1<<30),2)."GB";
  if( (!$unit && $size >= 1<<20) || $unit == "MB")
    return number_format($size/(1<<20),2)."MB";
  if( (!$unit && $size >= 1<<10) || $unit == "KB")
    return number_format($size/(1<<10),2)."KB";
  return number_format($size)." bytes";
}

I'm using this method:

function byteConvert($bytes)
{
    if ($bytes == 0)
        return "0.00 B";

    $s = array('B', 'KB', 'MB', 'GB', 'TB', 'PB');
    $e = floor(log($bytes, 1024));

    return round($bytes/pow(1024, $e), 2).$s[$e];
}

works great in o(1).

There is great example by Jeffrey Sambells:

function human_filesize($bytes, $dec = 2) 
{
    $size   = array('B', 'kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB');
    $factor = floor((strlen($bytes) - 1) / 3);

    return sprintf("%.{$dec}f", $bytes / pow(1024, $factor)) . @$size[$factor];
}

print human_filesize(filesize('example.zip'));

A pretty short 3 lines method that I use (1024 = 1KB) and supports from KB to YB is the following one:

<?php 

/**
 * Converts a long string of bytes into a readable format e.g KB, MB, GB, TB, YB
 * 
 * @param {Int} num The number of bytes.
 */
function readableBytes($bytes) {
    $i = floor(log($bytes) / log(1024));

    $sizes = array('B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB');

    return sprintf('%.02F', $bytes / pow(1024, $i)) * 1 . ' ' . $sizes[$i];
}

// "1000 B"
echo readableBytes(1000);

// "9.42 MB"
echo readableBytes(9874321);

// "9.31 GB"
// The number of bytes as a string is accepted as well
echo readableBytes("10000000000");

// "648.37 TB"
echo readableBytes(712893712304234);

// "5.52 PB"
echo readableBytes(6212893712323224);

More info about these methods on this article.