How to find out chords of a song??

First, you must understand that it's not at all difficult. It's a bit like riding a bicycle. You have to do it to know how to do it. And just like riding a bicycle -

1. It's is easier than it seems
2. It just needs a bit of practice
3. It takes some time to learn
4. Tabbing is hard at first and gets easier as you progress
5. Once you learn how to tab a song by ear, you can't forget it
6. It's faster, if you have someone teach you how to
7. You enjoy the result in both cases

Prerequisites:

1. You must know the song well. You must have heard it a couple of times and must remember the basic tune.
2. You must know how to write in chords out in any standard notation
3. You must be patient
4. Make sure you know how to find out tab of a song . That will form our basic process.
5. You have to have an understanding of the sounds of typical chord structures, scales, chord progressions, transpositions and strum patterns. Get an idea of how a particular chord type sounds like - how the sound of a major chord is different from that of a minor chord. How adding a 7th note alters the sound of these chords. What is the difference in sound of a C major, a D major, etc. It goes on.
6. Develop an ear to judge the basic key (scale) of the song. The better your ear gets in differentiating one scale from another and one chord from another, the better you can actually guess these chords. This is why ear training is so important

What this tutorial teaches you:

1. How to find the scale / key of a song
2. How to find the chords of a song on a guitar

So, here's the process of finding the chords to a song yourself, by ear:

1. First listen to the song - this will get your mind to catch the original scale of the song.
2. Try humming the song - this will make you sing the notes of the song
3. Follow a process similar to tabbing, but try playing chords instead of notes. It's a bit more difficult than tabbing.
4. Now, comes the harder part - play the song and try to guess it's key by ear. Now, is it a major or a minor key? Songs in the major key will have a minor chord coming in for most of the song; major for major. These should occur to you on its own spontaneously. It's a subconscious process of tonal recognition. Now that you have guess the key and type of chord, you know one chord - Major or minor chord of a the scale you guessed. If you guessed it's a major scale song and the key is that of C, the primary chord becomes C major.
5. Now play that chord along with the song. It should click in with some parts. If it does - you've got the song by its ear!
6. Songs tend to follow common chord progressions. Know at least the common chord progressions. Try to fit your song into one of them. Generally it would fit and ease your load. In case it does not, keep trying different chords of that key (concept obtainable by knowing musical modes).
7. Listen for when the chords actually change. You may be confused by meters ending and beginning - a function of the time signature of the song. Listen for the pitch to change and not for the strum pattern to end. Chords may or may not change over every meter. Again a single meter may have several rapid chord changes.
8. For chords that are proving difficult try the following tricks:
   • Play the leads and try out chords containing the notes you just played over that part. Generally you will be playing a 2-4 note sequence that falls into the scale of the chord. Remember to pick a chord that is consistent with the key you're playing in (or at least a parallel key or a relative key). For example, if you played a the notes C, D and E (any order) over the section in question while your song is in C major or A minor scale, its probably a C major chord being played as the scale of C major consists of the notes C, D, E, F, G, A and B.
   • Try and listen for the changes in the bass. A change in base / bass is usually associated with a chord change and vice versa. This should also help you avoid unnecessary chord changes.
   • Listen to to the vocals and try and appreciate the changes in pitch. The vocal part tends to go mostly in parallel with your leads.
9. In case the chords don't seem to work out the musician may have been trying to create some tension or a change of key:
   • Try tour primary chord here again. the chord may not have changed though it may sound like it. The phenomenon of Shepherd's tones is well known. Older songs tend to have few chords.
   • Try chords a semitone (fret) higher or lower - sequences that contain chords belonging to other keys may occur. Like C-F-G#-C, E-E-F-E
   • Try playing a chord where the scale does not allow it. Songs are there that contain sequences such as C-A-F-G though A major does not fall in the key of C major like rest of the chords (Am does).
   • The key may have been raised up or down like at the end of the song 'I just called to say I love you' where the key sequentially rises from C# to D to D#.
   • The part may not contain any chords and it may be all percussion, like at the beginning of Hotel California
   • The song may be contain rare chords, as is seen in jazz numbers
10. Try and go with the simplest possible chord sequence you get. Don't be tempted to use fancy added chords unless you're sure and get over your fascination with suspended chords. In medicine there is a dictum - if you diagnose a rare condition, you'll be rarely correct - applies to this as well; Occram's razor is a powerful concept. try and reduce sequences to one requiring lowest effort yet conforming to the tune.
11. Sometimes the chord may seem partly correct - this often means that there is an added or suspended chord here. If the sound is characteristically harsh or alarming - you may have just found yourself a diminished or an augmented chord
12. Keep noting and correcting your work. Repeated sequences need not be chorded over and over again, saving your some time and effort. Most songs will have a fixed key, a verse progression and a related chorus progression, how ever long it may be. There may or may not be an additional bridge section. This is because it's on song and not a chain of songs. This is going to make your work easier. This is also the reason why songs online tend to be written out in 'Verse, Chorus and Bridge' sections. Some sections will be harder than others.
13. Once you've got a good draft, check it by playing along with the track.
14. Make passes to make subtle changes that you may have missed