Code:
NSString *string = ...;
CGSize stringSize = [string sizeWithFont:[UIFont boldSystemFontOfSize:kTextFieldFontSize] constrainedToSize:CGSizeMake(320, 9999) lineBreakMode:UILineBreakModeWordWrap];
Then you could use the stringSize however you want, the key is in 9999 as a height.
You would rarely find any text view rect with more than 9999 as a height. Unless if it's an article or something.
Currently, I can not find any way to calculate it without constraint.
