How to Get Screen Size of Device

Get screen width and height in Android

Using this code, you can get the runtime display's width & height:

DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
int height = displayMetrics.heightPixels;
int width = displayMetrics.widthPixels;

In a view you need to do something like this:

((Activity) getContext()).getWindowManager()
                         .getDefaultDisplay()
                         .getMetrics(displayMetrics);

In some scenarios, where devices have a navigation bar, you have to check at runtime:

public boolean showNavigationBar(Resources resources)
{
    int id = resources.getIdentifier("config_showNavigationBar", "bool", "android");
    return id > 0 && resources.getBoolean(id);
}

If the device has a navigation bar, then count its height:

private int getNavigationBarHeight() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
        DisplayMetrics metrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        int usableHeight = metrics.heightPixels;
        getWindowManager().getDefaultDisplay().getRealMetrics(metrics);
        int realHeight = metrics.heightPixels;
        if (realHeight > usableHeight)
            return realHeight - usableHeight;
        else
            return 0;
    }
    return 0;
}

So the final height of the device is:

int height = displayMetrics.heightPixels + getNavigationBarHeight();

How to get screen size of device?

If you want the display dimensions in pixels you can use this code:

Display display = getWindowManager().getDefaultDisplay(); 
int width = display.getWidth();
int height = display.getHeight();

Then you can add condition that compares the height to satisfy your needs.

In inches:

DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
double x = Math.pow(dm.widthPixels/dm.xdpi,2);
double y = Math.pow(dm.heightPixels/dm.ydpi,2);
double screenInches = Math.sqrt(x+y);
Log.d("debug","Screen inches : " + screenInches);

How to get screen dimensions as pixels in Android

If you want the display dimensions in pixels you can use getSize:

Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
int width = size.x;
int height = size.y;

If you're not in an Activity you can get the default Display via WINDOW_SERVICE:

WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();

If you are in a fragment and want to acomplish this just use Activity.WindowManager (in Xamarin.Android) or getActivity().getWindowManager() (in java).

Before getSize was introduced (in API level 13), you could use the getWidth and getHeight methods that are now deprecated:

Display display = getWindowManager().getDefaultDisplay(); 
int width = display.getWidth();  // deprecated
int height = display.getHeight();  // deprecated

For the use case, you're describing, however, a margin/padding in the layout seems more appropriate.

Another way is: DisplayMetrics

A structure describing general information about a display, such as its size, density, and font scaling. To access the DisplayMetrics members, initialize an object like this:

DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);

We can use widthPixels to get information for:

"The absolute width of the display in pixels."

Example:

Log.d("ApplicationTagName", "Display width in px is " + metrics.widthPixels);

API level 30 update

final WindowMetrics metrics = windowManager.getCurrentWindowMetrics();
 // Gets all excluding insets
 final WindowInsets windowInsets = metrics.getWindowInsets();
 Insets insets = windowInsets.getInsetsIgnoringVisibility(WindowInsets.Type.navigationBars()
         | WindowInsets.Type.displayCutout());

 int insetsWidth = insets.right + insets.left;
 int insetsHeight = insets.top + insets.bottom;

 // Legacy size that Display#getSize reports
 final Rect bounds = metrics.getBounds();
 final Size legacySize = new Size(bounds.width() - insetsWidth,
         bounds.height() - insetsHeight);

How to Determine Screen Height and Width

You can use:

double width = MediaQuery.of(context).size.width;
double height = MediaQuery.of(context).size.height;

To get height just of SafeArea (for iOS 11 and above):

var padding = MediaQuery.of(context).padding;
double newheight = height - padding.top - padding.bottom;

Get the device width in javascript

You can get the device screen width via the screen.width property.
Sometimes it's also useful to use window.innerWidth (not typically found on mobile devices) instead of screen width when dealing with desktop browsers where the window size is often less than the device screen size.

Typically, when dealing with mobile devices AND desktop browsers I use the following:

 var width = (window.innerWidth > 0) ? window.innerWidth : screen.width;

Get screen resolution on a mobile website

You can perhaps use the screen object:

var w = screen.width;
var h = screen.height;

Update - Try to use it with the window.devicePixelRatio:

var ratio = window.devicePixelRatio || 1;
var w = screen.width * ratio;
var h = screen.height * ratio;

How to get android device screen size?

try this code to get screen size in inch

DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
int width=dm.widthPixels;
int height=dm.heightPixels;
double wi=(double)width/(double)dm.xdpi;
double hi=(double)height/(double)dm.ydpi;
double x = Math.pow(wi,2);
double y = Math.pow(hi,2);
double screenInches = Math.sqrt(x+y);

How to get screen size from C# code to XAML?

You can get the device info by Xamarin.Essentials: Device Display Information, create a struct called Constant and define the ScreenWidth and ScreenHeight there.

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();

        // Get Metrics
        var mainDisplayInfo = DeviceDisplay.MainDisplayInfo;

        // Orientation (Landscape, Portrait, Square, Unknown)
        var orientation = mainDisplayInfo.Orientation;

        // Rotation (0, 90, 180, 270)
        var rotation = mainDisplayInfo.Rotation;

        // Width (in pixels)
        var width = mainDisplayInfo.Width;

        // Height (in pixels)
        var height = mainDisplayInfo.Height;

        // Screen density
        var density = mainDisplayInfo.Density;

    }
}

public struct Constant
{
    public static double ScreenWidth = DeviceDisplay.MainDisplayInfo.Width / DeviceDisplay.MainDisplayInfo.Density;
    public static double ScreenHeight = DeviceDisplay.MainDisplayInfo.Height / DeviceDisplay.MainDisplayInfo.Density;
}

Use it in xaml:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             xmlns:local="clr-namespace:App105"
             x:Class="App105.MainPage">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="{Binding Source={x:Static local:Constant.ScreenWidth}}" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Label Text="Top Left" BackgroundColor="Red" Grid.Row="0" Grid.Column="0" />
        <Label Text="Top Right" BackgroundColor="Blue" Grid.Row="0" Grid.Column="1" />
        <Label Text="middle Left" BackgroundColor="Green" Grid.Row="1" Grid.Column="0" />
        <Label Text="middle Right" BackgroundColor="Yellow" Grid.Row="1" Grid.Column="1" />
        <Label Text="Bottom Left" BackgroundColor="Orange" Grid.Row="2" Grid.Column="0" />
        <Label Text="Bottom Righ" BackgroundColor="Pink" Grid.Row="2" Grid.Column="1" />
    </Grid>

</ContentPage>