Swift : Is it possible to set TextView limit depending on TextView width and height

Question

I have a textview and I set a text limit. Now I need a different way to set text limit. This textview height and width will change for every iPhone model. I want to set the limit as textview width and height. How can I do this ?

My code:

func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool {

return count(tweetTextView.text) + (count(text) - range.length) <= limit

}