Sort a custom post type array numerically

get_terms function will return an array of object. Each of them has term_id field which contains id of a term. Just use it instead of slug and you will have what you need:

<?php $terms = get_terms("ratios");
if ( $count($terms) > 0 ){
 foreach ( $terms as $term ) {
     echo "<option value="" . $term->term_id . "">" . $term->name . "</option>";
 }
}?>
</select>