How To Set Minimum Password Length In PHP Scripts Using strlen()

i want be able to make my login page more secure, i have seen some users they are entering and submitting very short passwords on their forms and i want to make it longer, like fore example, there was this subscriber who's password was only one character, i want to make so at least it should be 6 characters or more but not less.

if you can help me how to do this on my php script, thanks

<?php
if(strlen($password) < 6){
	echo 'ERROR: password is too short';
}else{
	echo 'Congratulations! Your password is secured';
}
?>