The default typeface for Android is Roboto.
Refer to Google's Material Design System for the type scale:
Material Design
Build beautiful, usable products faster. Material Design is an adaptable system—backed by open-source code—that helps teams build high quality digital experiences.
We have defined two additional styles for our type scale:
Name
Size
Weight
Letter spacing
Line height
Headline 7
16px
Medium
0.4px
24px
Headline 8
14px
20px