- substr: documentation ( source)
- strpos: documentation ( source)
<?php
$row["height"] = '(163 cm)';
$string= $row['height'];
$pos1 = strpos($string, "(");
$pos2 = strpos($string, "cm", $pos1);
$text = substr($string,$pos1+1,$pos2-2+$pos1);
echo $text;
?>