The below snippet with tell you the percentage of capital letters , lowercase letters or both. It will only take into account letters in the string being checked.

;http://www.hawkee.com/snippet/3325/ ( based off of )
;--- Usage ----------------
;--- $iscaps(string).up <-- %caps
;--- $iscaps(string).low <-- %lowercase
;--- $iscaps(string).ul <-- %caps , %lowercase
;--------------------------

Based on code made by Saeed