How to find scale of any song

I would not call this a professional way, but this is actually the way I casually used to find the scale of any song. This does not require you to have a well-developed ear. But you should be able to distinguish whether the notes are flowing together or clashing each other. As I told that this does not require a professional ear, this method is quite easy and any one playing guitar for few months sincerely should be able to pick up this method. Look at the shape given below.

Now play the song you wish to analyze scale wise. Play this shape over the song starting from any fret you like. This shape is not a magic shape but is taken from the shapes of the major scale. While playing this shape, if you find that this does not fit the song, shift one fret and try. At max, you will need to try this thing twelve times. But this will take you less than a minute (unless you are tone-deaf).When you find the correct fret where the notes are really following the song, you are done. The square marked note will give you the root note of the major scale and the triangular one will give you the root note of the relative minor scale.Generally most songs are written in major or minor scales. But this method works well for modal progressions as well. You only need to develop your ear a little bit so that you can pick out the note where the progression resolves completely. If you don’t know about modes, you should visit the lesson on modes which is already written on this site.