$re = '/\d*\s?\d+\/\d+"*\s*(in|")\sx\s\d*\s?\d+\/\d+"*\s*(in|")(*SKIP)(*FAIL)|\d*\s?\d+\/\d+"*\s*(in|")/m';
$str = 'A product description with 12 1/2" in it.
Product description with 19 3/4" x 19 5/8" in it.';
$subst = " ";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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