formatSize.php

<?php

function formatSize($bytes, $force_unit = null, $format = null, $si = true)
{
    // Format string
    $format = ($format === null) ? '%01.2f %s' : (string) $format;
 
    if (($si == false) || (strpos($force_unit, 'i') !== false)) {
        // IEC prefixes (binary)
        $units = array('B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB');
        $mod   = 1024;
    } else {
        // SI prefixes (decimal)
        $units = array('B', 'kB', 'MB', 'GB', 'TB', 'PB');
        $mod   = 1000;
    }
 
    // Determine unit to use
    if (($power = array_search((string) $force_unit, $units)) === false) {
        $power = ($bytes > 0) ? floor(log($bytes, $mod)) : 0;
    }
 
    return sprintf($format, $bytes / pow($mod, $power), $units[$power]);
}

// Testing...
var_dump(formatSize(1048576 * 1.75)); // 1.84 MB
var_dump(formatSize(1048576 * 1.75, null, null, false)); // 1.75 MB
var_dump(formatSize(1048576 * 1.75, 'kB')); // 1835.01 kB
var_dump(formatSize(1048576 * 1.75, 'KiB')); // 1792.00 KiB
var_dump(formatSize(1048576 * 1.75, 'KiB', '%d %s')); // 1792 KiB