A simple way to adjust the size of an UILabel to fit its contents by changing height only. Supports attributed strings.

UILabel+SizeToFit.h

//
//  UILabel+SizeToFit.h
//
//  Created by Maksym Huk on 4/4/13.
//  Copyright (c) 2013 Maksym Huk. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UILabel (SizeToFit)

- (void)sizeToFitByChangingHeight;

@end

UILabel+SizeToFit.m

//
//  UILabel+SizeToFit.m
//
//  Created by Maksym Huk on 4/4/13.
//  Copyright (c) 2013 Maksym Huk. All rights reserved.
//

#import "UILabel+SizeToFit.h"

@implementation UILabel (SizeToFit)

- (void)sizeToFitByChangingHeight
{
    CGRect frame = self.frame;
    CGSize size = [self sizeThatFits:CGSizeMake(frame.size.width, CGFLOAT_MAX)];
    frame.size.height = size.height;
    self.frame = frame;
}

@end