Dependency:var dp = Android.App.Application.Context.Resources.DisplayMetrics.Density;
var dp = Android.App.Application.Context.Resources.DisplayMetrics.Density;
var dp = Xamarin.Essentials.DeviceDisplay.MainDisplayInfo.Density;
If you have definite Size, use the dependency which shared above to get the device density which vary device to device and multiply it with your value.
label.FontSize = ConstantValue*dp
Otherwise, if you are using Xamarin.Essentials nuget in your application, refer the above code example.
If you are aware of font type, you can choose a required from the NamedSize where framework itself handle everything.
For Code behind refer the below code snippet.
label.FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Label));
For XAML refer below image.
Also, refer the below documentation.
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