How to detect the Windows 10 scale factor using C#?

Question

If you are having trouble reading text, recognizing icons and navigating apps because your high-resolution display makes everything look so tiny, then you need to check out Windows 10's scaling options. Go to Settings > System > Display and you'll find an option for Scale and layout. Windows will recommend a percentage. I want to use C# to get this value for "Scale and layout", I found that it's not the old DPI value (The LogPixels located on HKEY_CURRENT_USER\Control Panel\Desktop).

Answer 1

Please try the following code to get this percentage value.

        public static int GetWindowsScaling()  
        {  
            return (int)(100 * Screen.PrimaryScreen.Bounds.Width / SystemParameters.PrimaryScreenWidth);  
        }  

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Answer 2

No, it return 100 if restart program.

Answer 3

Also being late in the game, I would like to hint on two approaches that also work with WinForms. Which approach to take depends on the use case.

Approach A: Control.PreferredSize

Each control has a "designed" size, typically done with default scaling, i.e. 100%. Let's take a simple auto-sized label, e.g. 116 pixels wide and 13 pixels in height. Break the first time the parent's Paint event is invoked: At 125%, the label's PreferredSize reports e.g. {Width = 155 Height = 17}. Hmm... 133% rather than 125%? AutoScaleMode.Font apparently takes other things into account.

Now let's do the same with a control that has no text, e.g. 245 pixels wide and 295 pixels in height. After InitializeComponent() , the control's constructor will still state these values. Again break the first time the parent's Paint event is invoked: At 125%, the control's PreferredSize report e.g. {Width = 342 Height = 363}. The width is limited by the parent, by the height is free to scale, 363/295 = 1.23, i.e. pretty close to the 125% settings.

While this approach doesn't give the exact scaling value, it gives exact values how controls get scaled by WinForms.

Approach B: Control.DeviceDpi

According to https://learn.microsoft.com/en-us/windows/win32/learnwin32/dpi-and-device-independent-pixels, 100% scaling is 96 DPI:

const int DefaultDpi = 96;

Any form or control can easily calculate the current scaling:

var scaling = (float)DeviceDpi / DefaultDpi; // = 1.25 with a 125% setting

The default of 96 DPI should also works on Linux, e.g. https://wiki.archlinux.org/title/HiDPI.