$re = '/(?<!\S)\d+(?:,\d+)? ?x ?\d+(?:,\d+)?(?: ?x ?\d+(?:,\d+)?)*/';
$str = 'Square 10 x 3 x 5 mm
Round 23/22; 24,9 x 12,2 x 12,3
Square 10x2
Straight 10x2mm
Round 23/22; 24,9x12,2';
preg_match_all($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