Unity Canvas Buttons gets tiny when Build

Question

I am working with Unity 5, and when I add Canvas Button the button get smaller this is how it looks like before build Before Build to an Apk

and after build on my Lg g3:

Answer 1

As seen on your screenshots, the button has a fixed size in pixels. and your mobile screen probably has a higher screen resolution.

Set the Canvas Scaler to something other than Constant Pixel Size as this Makes UI elements retain the same size in pixels regardless of screen size.

scale with screensize would in this case be more fitting. As it Makes UI elements bigger the bigger the screen is.

as per Unity Documentation