As i see all UMG widgets have aspect ratio - Full screen.
How to create Widget with size of only Progress bar for example? so i could use it as separate ProgressBarWidget?
Size of widgets is mostly determined by parents - the designer just so happens to currently only simulate a full screen view of the widget. If you were to just delete the canvas root and drop a progress bar down it will look ridiculous, but if you reuse that new widget in another widget it will default to the desired size of the root widget (the progress bar) or lets say a horizontal box with some text and a progress bar…or whatever you use 
Cheers,
Nick