[UIApplication sharedApplication].statusBarFrame.size.height. But since all sizes are in points, not in pixels, status bar height always equals 20.

Update. Seeing this answer being considered helpful, I should elaborate.

Status bar height is, indeed, equals 20.0f points except following cases:

• status bar has been hidden with setStatusBarHidden:withAnimation: method and its height equals 0.0f points;
• as @Anton here pointed out, during an incoming call outside of Phone application or during sound recording session status bar height equals 40.0f points.

There's also a case of status bar affecting the height of your view. Normally, the view's height equals screen dimension for given orientation minus status bar height. However, if you animate status bar (show or hide it) after the view was shown, status bar will change its frame, but the view will not, you'll have to manually resize the view after status bar animation (or during animation since status bar height sets to final value at the start of animation).

Update 2. There's also a case of user interface orientation. Status bar does not respect the orientation value, thus status bar height value for portrait mode is [UIApplication sharedApplication].statusBarFrame.size.height (yes, default orientation is always portrait, no matter what your app info.plist says), for landscape - [UIApplication sharedApplication].statusBarFrame.size.width. To determine UI's current orientation when outside of UIViewController and self.interfaceOrientation is not available, use [UIApplication sharedApplication].statusBarOrientation.

Update for iOS7. Even though status bar visual style changed, it's still there, its frame still behaves the same. The only interesting find about status bar I got – I share: your UINavigationBar's tiled background will also be tiled to status bar, so you can achieve some interesting design effects or just color your status bar. This, too, won't affect status bar height in any way.

You should never hardcode the exact value of the height at any point in your code.

As long as you use default UI components (UINavigationController / UITableView / UICollectionView / etc.) you usually don't need to worry about the status bar height at all. These ViewControllers should layout correctly on any device and any orientation.

If you do have custom layout needs, you should refer to the safeAreaLayoutGuide on UIView, instead of hardcoding a height: https://developer.apple.com/documentation/uikit/uiview/2891102-safearealayoutguide?language=objc

But to make this answer complete - the size of the status bar is different on different devices and different orientations:

• Most devices up to the iPhone X have a 20pt height in portrait & landscape.
  (20px, 40px, 60px in @1x, @2x, @3x)
• On iPhone X in portrait it's 44pt (so 44px, 88px, 132px accordingly).
  In landscape the height is different though.

If you're using Expo you can use Constants.statusBarHeight.

import Constants from 'expo-constants';
const statusBarHeight = Constants.statusBarHeight;

If you're using Vanilla React Native with React Navigation you can use the following:

import { useSafeAreaInsets } from 'react-native-safe-area-context';
const insets = useSafeAreaInsets();
const statusBarHeight = insets.top;

See: https://reactnavigation.org/docs/handling-safe-area/#use-the-hook-for-more-control

Sample Code:

import * as React from 'react';
import { Text, View, StatusBar } from 'react-native';
import Constants from 'expo-constants';
import { useSafeAreaInsets, SafeAreaProvider } from 'react-native-safe-area-context';

export default function App() {
  return (
    <SafeAreaProvider>
      <ChildScreen />
    </SafeAreaProvider>
  );
}

function ChildScreen() {
  const insets = useSafeAreaInsets();
  
  return (
    <View style={{ flex: 1, justifyContent: 'center'}}>
      <Text>
        {insets.top}
      </Text>
      <Text>
        {Constants.statusBarHeight}
      </Text>
      <Text>
        {StatusBar.currentHeight ?? 'N/A'}
      </Text>
    </View>
  );
}

Output:

Live code: https://snack.expo.dev/@dcangulo/statusbarheight

As the warning hints, you can access the statusBarManager which has a statusBarFrame property. This is defined on your UIWindow's windowScene.

let height = view.window?.windowScene?.statusBarManager?.statusBarFrame.height ?? 0

Is there any problems with Swift 2.x:

UIApplication.sharedApplication().statusBarFrame.size.height

Swift 3 or Swift 4:

UIApplication.shared.statusBarFrame.height

Make sure UIKit is imported

import UIKit

In iOS 13, you will get a deprecated warning"

'statusBarFrame' was deprecated in iOS 13.0: Use the statusBarManager property of the window scene instead.

To fix this:

let height = view.window?.windowScene?.statusBarManager?.statusBarFrame.height ?? 0

The display on iPhone X, however, is 145pt taller than a 4.7" display, resulting in roughly 20% additional vertical space for content.

for more information you get HIG for iphone X from apple documents and detail description in here1 and here2

status bar height

previously 20pt, now 44pt

Because of the sensors on top of the display, the new status bar is split in 2 parts. If your UI is doing something special with that space (previously 20pt high, now 44pt), because it will be taller on the iPhone X. Make sure that it can be dynamically changed in height. A great thing is that the height won’t be changed if a user makes a phone call or is using a navigation app, which was previously the case on other iPhones.

portrait

Navigation bar height as normal 88 and large title time 140

• Standard title - 44pt (88pt with Status Bar)
• Large title - 140pt
• bottom bar - 34pt

Landscape

• Standard title - 32pt
• bottom bar - 21pt

You are right, 20 pixel on the iPad. See also this forum posting for further links to back that claim up.