$re = '/\b(?:1,[2-9]|(?:[2-9]|[1-9]\d{1,2}),\d)\d\d,\d{3} K/m';
$str = '1,100,000 K
1,200,000 K
1,455,204 K
1,800,000 K
2,000,000 K
15,000,000 K';
preg_match_all($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