Here is xaml (an image in stacklayout). Everything is logical: I set Aspect to AspectFit and HorizontalOptions to FillAndExpand. Width of image must fill the width of stackl
Try using CachedImage from FFImageLoading NuGet package
MyPage.xaml
This will results image trying to horizontally fill the container and to automatically generate the width while maintaining its aspect.
Add this line of code to MainActivity.xaml after global::Xamarin.Forms.Forms.Init(this, bundle);
CachedImageRenderer.Init(true);
Example can be found here