UILabel+dynamicSizeMe.h

@interface UILabel (dynamicSizeMe)

-(float)resizeToFit;
-(float)expectedHeight;
-(void)resizeToStretch;
-(float)expectedWidth;

@end

UILabel+dynamicSizeMe.m

#import "UILabel+dynamicSizeMe.h"

@implementation UILabel (dynamicSizeMe)

-(float)resizeToFit
{
    float height = [self expectedHeight];
    CGRect newFrame = [self frame];
    newFrame.size.height = height;
    [self setFrame:newFrame];
    return newFrame.origin.y + newFrame.size.height;
}

-(float)expectedHeight
{
    [self setNumberOfLines:0];
    [self setLineBreakMode:UILineBreakModeWordWrap];

    CGSize maximumLabelSize = CGSizeMake(self.frame.size.width,9999);
    
    CGSize expectedLabelSize = [[self text] sizeWithFont:[self font] 
                                            constrainedToSize:maximumLabelSize
                                            lineBreakMode:[self lineBreakMode]]; 
    return expectedLabelSize.height;
}

-(void)resizeToStretch
{
    float width = [self expectedWidth];
    CGRect newFrame = [self frame];
    newFrame.size.width = width;
    [self setFrame:newFrame];
}

-(float)expectedWidth
{
    [self setNumberOfLines:1];
    
    CGSize maximumLabelSize = CGSizeMake(9999,self.frame.size.height);
    
    CGSize expectedLabelSize = [[self text] sizeWithFont:[self font]
                                       constrainedToSize:maximumLabelSize
                                           lineBreakMode:[self lineBreakMode]];
    return expectedLabelSize.width;
}

@end