How to calculate UILabel height dynamically?

Try this

// UILabel *myLabel;

CGSize labelSize = [myLabel.text sizeWithFont:myLabel.font 
                            constrainedToSize:myLabel.frame.size 
                                lineBreakMode:NSLineBreakByWordWrapping];

CGFloat labelHeight = labelSize.height;


int lines = [myLabel.text sizeWithFont:myLabel.font 
                     constrainedToSize:myLabel.frame.size 
                         lineBreakMode:NSLineBreakByWordWrapping].height/16; 
             // '16' is font size

or

int lines = labelHeight/16;

NSLog(@"lines count : %i \n\n",lines);  

or

int lines = [myLabel.text sizeWithFont:myLabel.font 
                     constrainedToSize:myLabel.frame.size 
                         lineBreakMode:UILineBreakModeWordWrap].height /myLabel.font.pointSize; //fetching font size from font

By Using Categories, Just Create the category class named as

UILabel+UILabelDynamicHeight.h

UILabel+UILabelDynamicHeight.m

No more tension about the height calculation. Please review the below implementation.

Updates for iOS7 & Above,iOS 7 below : Dynamically calculate the UILabel height

#define SYSTEM_VERSION_EQUAL_TO(v)                  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)
#define SYSTEM_VERSION_GREATER_THAN(v)              ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)
#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)
#define iOS7_0 @"7.0"

UILabel+UILabelDynamicHeight.h

#import <UIKit/UIKit.h>
@interface UILabel (UILabelDynamicHeight)

#pragma mark - Calculate the size the Multi line Label
/*====================================================================*/

    /* Calculate the size of the Multi line Label */

/*====================================================================*/
/**
 *  Returns the size of the Label
 *
 *  @param aLabel To be used to calculte the height
 *
 *  @return size of the Label
 */
 -(CGSize)sizeOfMultiLineLabel;

@end

UILabel+UILabelDynamicHeight.m

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


#pragma mark - Calculate the size,bounds,frame of the Multi line Label
/*====================================================================*/

/* Calculate the size,bounds,frame of the Multi line Label */

/*====================================================================*/
/**
 *  Returns the size of the Label
 *
 *  @param aLabel To be used to calculte the height
 *
 *  @return size of the Label
 */
-(CGSize)sizeOfMultiLineLabel{

    //Label text
    NSString *aLabelTextString = [self text];

    //Label font
    UIFont *aLabelFont = [self font];

    //Width of the Label
    CGFloat aLabelSizeWidth = self.frame.size.width;


    if (SYSTEM_VERSION_LESS_THAN(iOS7_0)) {
        //version < 7.0

        return [aLabelTextString sizeWithFont:aLabelFont
                            constrainedToSize:CGSizeMake(aLabelSizeWidth, MAXFLOAT)
                                lineBreakMode:NSLineBreakByWordWrapping];
    }
    else if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(iOS7_0)) {
        //version >= 7.0

        //Return the calculated size of the Label
        return [aLabelTextString boundingRectWithSize:CGSizeMake(aLabelSizeWidth, MAXFLOAT)
                                              options:NSStringDrawingUsesLineFragmentOrigin
                                           attributes:@{
                                                        NSFontAttributeName : aLabelFont
                                                        }
                                              context:nil].size;

    }

    return [self bounds].size;

}
@end