Returns formatted file size

function-file_size_format.php

<?php

/**
 * Returns formatted file size
 *
 * Inspired by {@link http://betterwp.net/wordpress-tips/size_format/}, modified
 * to work outside of WordPress environment.
 *
 * @param   int     $bytes      Size in bytes
 * @param   int     $decimals   Number of decimal places
 * @returns string
 *
 */
function file_size_format($bytes, $decimals = 0, $dec_point = '.', $thousands_sep = ',')
{
    $quant = array(
        // ========================= Origin ====
        'TB' => 1099511627776,  // pow( 1024, 4)
        'GB' => 1073741824,     // pow( 1024, 3)
        'MB' => 1048576,        // pow( 1024, 2)
        'kB' => 1024,           // pow( 1024, 1)
        'B ' => 1,              // pow( 1024, 0)
    );

    foreach ($quant as $unit => $mag) {
        if ( doubleval($bytes) >= $mag ) {
            return function_exists('number_format_i18n') ? number_format_i18n( $bytes / $mag, $decimals ) . ' ' . $unit : number_format( $bytes / $mag, $decimals, $dec_point, $thousands_sep) . ' ' . $unit;
        }
    }

    return false;
}