Smallest phone screen to design for

I am developing an android app, and I was wondering the smallest screen size I should design for... I covered my bases with horizontal scrolling, but implementing horizontal and vertical scrolling without code breaking seems to be a pain, so I was wondering what the smallest reasonable screen size would be for an android phone...

Thanks!

P.S. I did see this question, but it didn't really answer my question, since it was about laptop screen sizes... Also, in android studio, the dimensions are listed like this: 480x800, etc. What do these numbers mean?