One of the most common questions from students is “how do I figure out what key a song is in?” Colin gets asked this all the time, and the answer depends on what tools you have — your ear, your knowledge of guitar scales, and how well you know your chord relationships.

Figure Out the Chords First

Colin’s approach starts with the chords. Figure out the chord changes by ear, then use those chords to identify the key. Once you know a few of the chords in the song, you can match them against the I-IV-V pattern. For example, if you hear E, A, and B — that’s I-IV-V in the key of E. If you hear C#m, A, E, and B — the C#m is the relative minor (the vi chord), and you’re still in E major.

The first chord isn’t always the key. Boston’s “Peace of Mind” starts on C#m but the key is actually E major — the C#m is just the relative minor tonic. You have to look at the full set of chord changes, not just the first one you hear.

Use a Scale to Confirm

Once you have a guess at the key, play a major or minor scale over the chord progression. If every note in the scale sounds good against the chords, you’ve found your key. If some notes clash, try a different key.

The diatonic scale (major or minor) works best for this because it gives you the complete picture — all seven notes. The pentatonic will get you close but it’s missing two notes, so it’s not as definitive. Colin recommends the minor diatonic as the most practical starting point since most rock and blues leans minor.

Watch Out for Pitch Issues

Here’s something that trips up a lot of players: older recordings are sometimes out of standard pitch. When songs were recorded on reel-to-reel tape, producers would speed up the tape to brighten the sound, which raised the pitch. Chuck Berry’s “Johnny B. Goode” is a famous example — Keith Richards thought it was in A, Chuck Berry said G. They were both right, depending on whether you matched the tape or the original live key.

Tom Petty’s “Mary Jane’s Last Dance” is another one — it sits between A minor and A# minor. Not quite either. That happened in mastering.

The fix is simple: tune your guitar to match the recording before you start. If the song is slightly sharp or flat, adjust your tuning to match. You can’t figure out a song by ear if your guitar is out of tune with the track.

Major vs Minor — Hear the Difference

You also need to train your ear to hear the difference between major and minor chords. Major sounds brighter and happier. Minor sounds darker and sadder. Once you can reliably tell them apart, identifying the key gets much easier because you can narrow down whether you’re in a major or minor key from the first chord change.

For more on how major and minor keys relate to each other, check out the relative major/minor scales lesson. And if you want to put this theory into practice over real progressions, the Guitar Improvising Secrets course covers it in depth.