I want to develop application with single binary for Android device and for Android tablets with target android 2.1 version.
My orientation also depends upon whether app is running on device or on tablet.
So i just want to know, is there any specification like tablet should be minimum of “X” inches.
There is heaps of information on screen sizes and each device can be different so you should use the Android standards talked about here to figure out exactly what screen you are dealing with and react accordingly. There are no hard and fast “atleast X inches” rules; just different screen sizes of different resolutions. You can use the Android manifest to restrict the screen sizes to just the ones that you want to support.