GUI Button : Changing Position Based On Screen Size

I am new to Unity and I am developing a simple 2D game for android. I created a 3 button and on my game view its perfect on position,size every thing but when I build the game and install it on my Samsung galaxy S3 the first button located in the bottom left corner was good but small and the second and third button located in the bottom right corner next to each other the second wan was good but also small but the third one was out the screen I can’t even see it. So how can I fix that

Am using JavaScript

Use the properties of Screen like

Screen.width
//And
Screen.height

These are fixed for your device.
For example,

GUI.Button(new Rect(Screen.width * 0.1,Screen.height * 0.1,Screen.width* 0.2,Screen.height * 0.2),"First");

This will make a button of 1/5 width of screen and 1/5 height of screen at 1/10th gap from the left of screen and 1/10th gap from the top of screen.
For extra details , check unity manual at the official unity site.

If this solves your problem, mark this question as solved.