Converts px to cm (with DPI) and variable precision

convert_px_to_cm.php

<?php

function get_cm_by_px($px, $dpi = 300, $precision = 2) {
    $comma = ','; // if US use '.'
    return number_format(2.54 * $pic->exif->size->height / $dpi , $precision, $comma,'') ;
}

Example:

1000px Photo = 8,47cm (if printed with 300DPI)

<?php
$px = '1000px';

function get_cm_by_px($px, $dpi = 300, $precision = 2) {
    $comma = ','; // if US use '.'
    return number_format(2.54 * (int)$px / $dpi , $precision, $comma,'') ;
}

var_dump(get_cm_by_px($px));

Result: (test with all PHP 4.3.0 - 5.6.0 versions) -> http://3v4l.org/Z1LmO