UILabel+ContentSize.h

#import <UIKit/UIKit.h>
 
@interface UILabel (ContentSize)
 
- (CGSize)contentSize;
 
@end

UILabel+ContentSize.m

#import "UILabel+ContentSize.h"
 
@implementation UILabel (ContentSize)

- (CGSize)contentSize {
   NSMutableParagraphStyle * paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    paragraphStyle.lineBreakMode = self.lineBreakMode;
    paragraphStyle.alignment = self.textAlignment;
    
    NSDictionary * attributes = @{NSFontAttributeName : self.font,
                                  NSParagraphStyleAttributeName : paragraphStyle};
    
    CGSize contentSize = [self.text boundingRectWithSize:self.frame.size
                                              options:(NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading)
                                           attributes:attributes
                                              context:nil].size;
    return contentSize;
}