Returns a CGSize for a multi-line string.

NSString+AdjustedSize.m

- (CGSize)adjustedSizeWithFont:(UIFont *)font fromDefaultSize:(CGSize)defaultSize {
    
    CGFloat additionalHeight = 0.0f;
    
    NSDictionary *attributes = @{NSFontAttributeName : font};
    
    CGRect rect = [self boundingRectWithSize:CGSizeMake(defaultSize.width, MAXFLOAT)
                                     options:NSStringDrawingUsesLineFragmentOrigin
                                  attributes:attributes
                                     context:nil];
    
    //Doesn't matter what the string is here. Just need to get the height of one line of text.
    CGRect singleLineRect = [@"X" boundingRectWithSize:CGSizeMake(defaultSize.width, MAXFLOAT)
                                               options:NSStringDrawingUsesLineFragmentOrigin
                                            attributes:attributes
                                               context:nil];
    
    additionalHeight -= CGRectGetHeight(singleLineRect);
    additionalHeight += CGRectGetHeight(rect);
    
    return CGSizeMake(defaultSize.width, defaultSize.height + ceil(additionalHeight));
}