$re = '/(?:(\w+))?\s?\b(\d+)\s?x\s?(\d+)\s?(cm)\b/';
$str = '
30 x 30 cm
30x30cm
30x30 cm
Ixxx 30x30cm
xxxx (30x30cm)
xxxx (30 x 30 cm)';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php