Dynamically changing font size of UILabel

Question

Single line:

factLabel.numberOfLines = 1;
factLabel.minimumFontSize = 8;
factLabel.adjustsFontSizeToFitWidth = YES;

The above code will adjust your text's font size down to (for example) 8 trying to fit your text within the label. numberOfLines = 1 is mandatory.

Multiple lines:

For numberOfLines > 1 there is a method to figure out the size of final text through NSString's sizeWithFont:... UIKit addition methods, for example:

CGSize lLabelSize = [yourText sizeWithFont:factLabel.font
                                  forWidth:factLabel.frame.size.width
                             lineBreakMode:factLabel.lineBreakMode];

After that you can just resize your label using resulting lLabelSize, for example (assuming that you will change only label's height):

factLabel.frame = CGRectMake(factLabel.frame.origin.x, factLabel.frame.origin.y, factLabel.frame.size.width, lLabelSize.height);

iOS6

Single line:

Starting with iOS6, minimumFontSize has been deprecated. The line

factLabel.minimumFontSize = 8.;

can be changed to:

factLabel.minimumScaleFactor = 8./factLabel.font.pointSize;

iOS7

Multiple lines:

Starting with iOS7, sizeWithFont becomes deprecated. Multiline case is reduced to:

factLabel.numberOfLines = 0;
factLabel.lineBreakMode = NSLineBreakByWordWrapping;
CGSize maximumLabelSize = CGSizeMake(factLabel.frame.size.width, CGFLOAT_MAX);
CGSize expectSize = [factLabel sizeThatFits:maximumLabelSize];
factLabel.frame = CGRectMake(factLabel.frame.origin.x, factLabel.frame.origin.y, expectSize.width, expectSize.height);

iOS 13 (Swift 5):

label.adjustsFontSizeToFitWidth = true
label.minimumScaleFactor = 0.5

minimumFontSize has been deprecated with iOS 6. You can use minimumScaleFactor.

yourLabel.adjustsFontSizeToFitWidth=YES;
yourLabel.minimumScaleFactor=0.5;

This will take care of your font size according width of label and text.

Single line- There are two ways, you can simply change.

1- Pragmatically (Swift 3)

Just add the following code

    yourLabel.numberOfLines = 1;
    yourLabel.minimumScaleFactor = 0.7;
    yourLabel.adjustsFontSizeToFitWidth = true;

2 - Using UILabel Attributes inspector

i- Select your label- Set number of lines 1.
ii- Autoshrink-  Select Minimum Font Scale from drop down
iii- Set Minimum Font Scale value as you wish , I have set 0.7 as in below image. (default is 0.5)

Based on @Eyal Ben Dov's answer you may want to create a category to make it flexible to use within another apps of yours.

Obs.: I've updated his code to make compatible with iOS 7

-Header file

#import <UIKit/UIKit.h>

@interface UILabel (DynamicFontSize)

-(void) adjustFontSizeToFillItsContents;

@end

-Implementation file

#import "UILabel+DynamicFontSize.h"

@implementation UILabel (DynamicFontSize)

#define CATEGORY_DYNAMIC_FONT_SIZE_MAXIMUM_VALUE 35
#define CATEGORY_DYNAMIC_FONT_SIZE_MINIMUM_VALUE 3

-(void) adjustFontSizeToFillItsContents
{
    NSString* text = self.text;

    for (int i = CATEGORY_DYNAMIC_FONT_SIZE_MAXIMUM_VALUE; i>CATEGORY_DYNAMIC_FONT_SIZE_MINIMUM_VALUE; i--) {

        UIFont *font = [UIFont fontWithName:self.font.fontName size:(CGFloat)i];
        NSAttributedString *attributedText = [[NSAttributedString alloc] initWithString:text attributes:@{NSFontAttributeName: font}];

        CGRect rectSize = [attributedText boundingRectWithSize:CGSizeMake(self.frame.size.width, CGFLOAT_MAX) options:NSStringDrawingUsesLineFragmentOrigin context:nil];

        if (rectSize.size.height <= self.frame.size.height) {
            self.font = [UIFont fontWithName:self.font.fontName size:(CGFloat)i];
            break;
        }
    }

}

@end

-Usage

#import "UILabel+DynamicFontSize.h"

[myUILabel adjustFontSizeToFillItsContents];

Cheers

It's 2015. I had to go to find a blog post that would explain how to do it for the latest version of iOS and XCode with Swift so that it would work with multiple lines.

1. set “Autoshrink” to “Minimum font size.”
2. set the font to the largest desirable font size (I chose 20)
3. Change “Line Breaks” from “Word Wrap” to “Truncate Tail.”

Source: http://beckyhansmeyer.com/2015/04/09/autoshrinking-text-in-a-multiline-uilabel/

Swift version:

textLabel.adjustsFontSizeToFitWidth = true
textLabel.minimumScaleFactor = 0.5