Reverse Engineering Voicings: Name That Chord!

Judging by the sheer number of "what chord is this?" posts on Facebook and Reddit, we could all use some help figuring out what to call that cool-sounding fingering we just came up with. If your voicing fits one of the 22 most common chord types, this method will get you the correct answer every time, even if you have no idea which note is the root.

Once you've worked through it, try the method on your own shapes with What Chord Is This? — a free tool that runs these same steps and shows every one of them, so you can check an answer or watch the process before you trust yourself with it.

Reverse engineering voicings: name that chord!

Have you ever stumbled upon a beautiful chord while noodling around, only to realize you have no idea what to call it? If Reddit and Facebook are any indication, that happens to guitar players a lot. In a previous lesson, I showed how to decode a chord name and figure out which notes belong to it, and in this lesson, I’m going to flip the script and show you how to take just about any chord fingering and figure out its proper name.

This technique builds on the interval counting method from my “Intervals: Guitar’s Secret Decoder Ring” YouTube video. If you haven’t watched that yet, you might want to review it first, but I’ll give you a quick recap of the most important points.

The method I’m about to show you is systematic, repeatable, and surprisingly quick once you get the hang of it. Let’s dive in.

A refresher on intervals

There are 12 possible intervals between two notes, each identified by the number of semitones between the origin note and the target note. In this lesson, all intervals will be measured from a lower-pitched note moving up to a higher-pitched note. Here’s a summary:

Interval (semitones)	Abbreviation	Name
0	R, P8	Root, unison, octave
1	m2, m9	Minor 2nd, minor 9th
2	2, 9	Major 2nd, major 9th
3	m3, #9	Minor 3rd, sharp 9
4	3	Major 3rd
5	P4, 11	Perfect 4th, 11th
6	#4, #11, b5	Tritone, augmented 4th, diminished 5th
7	P5	Perfect 5th
8	m6, m13, #5	Minor 6th, minor 13th, augmented 5th
9	6, 13, ♭♭7	Major 6th, major 13th, diminished 7th
10	m7	Minor 7th
11	7	Major 7th

For this method, you don’t need to know the names or abbreviations. All we need is to be able to measure the distance between two notes in semitones (or frets).

One simple way to do that is to use the fretboard as a ruler. Since the guitar is mostly tuned in 4ths (a five-semitone distance), we can count by fives as we move from string to string, staying on the same fret. We have to be a little bit careful when we move from the G string to the B string, since that interval is a major 3rd. You can either add four (instead of five) for that string, or move diagonally one fret toward the bridge. This is the familiar adjustment we make to take account of the warp.

Once we’ve accounted for the difference in strings, we add one for every fret as we move toward the bridge, or subtract one for every fret moved toward the nut.

Finally, if we get a total that is larger than 11, we subtract 12s until we get into the range 0-11. If we ever get a number less than zero, we add 12s until we get into the valid range.

Here is an example, so that you can test your understanding:

The seven-step method

To find the name of a chord from a voicing, there are seven steps.

Step 1: Assign zero to the lowest note in the voicing

First, identify the note on the lowest string that is part of the voicing. This is usually the lowest-pitched note in the voicing, but it doesn’t have to be. Assign this note the number 0. This will be our reference point for measuring all the other intervals, and it will be our first candidate for the root of the chord.

Step 2: Count semitones to each additional note

For each other note in the chord, count how many semitones it is above your reference note. As described above, count by fives when you move to the next higher string, and count by ones when you move along a string. Moving toward the bridge adds one, and moving toward the nut subtracts one. Don’t forget to move diagonally when you move from the G to the B string.

If your reference note isn’t the lowest note in the chord, it’s possible to end up with a negative number from this calculation. We’ll fix that in the next step.

As a practical example, let’s say you’re playing this shape:

Step 3: Simplify your interval set

Next, we need to reduce all intervals to a one-octave range, eliminate duplicates, and put the intervals in order. We can do this by:

• Subtracting 12 from any number greater than 11
• Adding 12 to any number less than 0
• Removing duplicate values
• Sorting the remaining numbers in ascending order

Here are the normalized numbers from the example:

After removing duplicate values and sorting the remaining numbers, our result is {0, 4, 7}.

Step 4: Match against the decoder ring

Every type of chord contains a specific set of intervals. Here is a list of the 22 most common chord types and their unique interval signatures:

Interval signature	Chord suffix	Note
{0, 2, 4, 5, 7, 9, 10}	13
{0, 2, 4, 5, 7, 10}	11
{0, 2, 4, 7}	add9
{0, 2, 4, 7, 10}	9
{0,2,7}	sus2
{0,3,4,7,10}	7#9
{0,3,6}	dim	Diminished triad
{0,3,6,9}	dim7
{0,3,6,10}	m7♭5, ø	Half-diminished
{0,3,7}	m	Minor triad
{0,3,7,9}	m6	Minor 6th
{0,3,7,10}	m7
{0,3,7,11}	m(maj7)
{0,4,5,7}	add11
{0,4,6,7,11}	maj7#11
{0,4,7}		Major triad
{0,4,7,9}	6	Major 6th
{0,4,7,10}	7	Dominant 7
{0,4,7,11}	maj7
{0,4,8}	aug, +	Augmented triad
{0,5,7}	sus4
{0,7}	5	Power chord

Our example chord has the signature {0,4,7}, which matches the major triad. To name the chord, start with the root note’s name and add on the chord suffix for the matching interval signature. Since the root is a G note and the chord suffix column is empty, we just call this a G chord.

If you get a perfect match, you can stop here, unless your chord matches one of six special-case chords:

1. If you matched an Augmented triad {0,4,8}, the root is not fully determined. Because the augmented triad is symmetric (there’s a major third distance between each pair of notes), any of the notes could be the root. Example: Caug = Eaug = G#aug.
2. The Diminished Seventh chord {0,3,6,9}, is also symmetrical (with minor third intervals), and any of the notes could be considered to be the root. Example: Cdim7 = E♭dim7 = Gbdim7 = Adim7.
3. A Major 6th {0,4,7,9} chord shares the exact same notes as a m7 chord built from the major 6th. Example: C6 = Am7.
4. Conversely, a m7 {0,3,7,10} shares the same notes as a 6 chord built on the minor 3rd. Example: Cm7 = E♭6.
5. A Minor 6th {0,3,7,9} chord shares the same notes as a m7♭5 built from the major 6th. Example: Cm6 = Am7♭5.
6. Conversely, a m7♭5 {0,3,6,10} chord shares the same notes as a m6 chord built from the minor 3rd. Example: Cm7♭5 = E♭m6.

In the ambiguous cases, you’ll need to call on additional music theory, using the context to choose the “correct” root, and that’s outside the scope of this lesson.

Step 5: Check for inversions

Sometimes you won’t find a perfect match in Step 4. That often means that the lowest note in the chord isn’t the root. In other words, you’re dealing with an inversion or slash chord. Here’s how to proceed:

1. Add 12 to your original “0” note and move it to the end of the list.
2. Take the new lowest value and subtract it from all the notes.
3. Try matching again with the decoder ring.
4. If you get a match, you’ve found the root, and the original lowest note becomes the bass note in slash notation.

Let’s say we had this chord:

The interval set is {0,3,8}. That doesn’t match any standard chord, so:

1. Move the 0 to the end and add 12: {3,8,12}
2. Subtract 3 from everything: {0,5,9}
3. Check the decoder ring

There’s still no match, so let’s continue…

Step 6: Continue iterating through possible roots

If you still don’t have a match, keep rotating through the notes. Each note in your chord could potentially be the root. For our {0,3,8} example, we arrived at {0,5,9}:

1. Move the 0 to the end and add 12: {5,9,12}
2. Subtract 5 from everything: {0,4,7}
3. This matches a major triad.

Step 7: Recover the root

Since it was our third attempt to match the chord that yielded a result, we can go back go the original interval set and know that the note represented by the third number in the signature is the root. In this case, the root is the note that’s 8 semitones above the lowest note. The note marked 8 in the chord diagram is a D#, and the lowest note is a G, so this is a D#/G chord.

Practical example

To drive this home, let’s do another example. Here’s a fairly common grip you may or may not recognize:

We treat the lowest note as the root and count the intervals:

We normalize the numbers and put them in increasing order to get: {0,3,6,8}.

This doesn’t match anything, so we perform a rotation, getting: {0,3,5,9}.

Still no match, so we rotate again, getting: {0,2,6,9}.

Still no match, so we rotate once more, getting: {0,4,7,10}.

This matches a dominant 7 chord, and we know that the fourth interval from the original set (8) is the root. That’s a D note, and the original red note is an F#, so this is a D7/F# chord.

What to do if this doesn’t work

This method works for almost all commonly-used chord fingerings, as well as many uncommon ones, but there are two things that can go wrong. Before you consider them, I recommend double-checking your semitone counting and the rotations you calculated. It’s easy to make a mistake along the way that will give you an invalid result.

If your math is correct, the first potential issue is that your chord voicing may be missing one or more notes. Looking at the decoder ring, notice that the 13 chord has seven notes in it (try playing that in standard tuning!). In jazz, the fifth of the chord (the 7 in the signature) is often omitted because it doesn’t add much color to the chord. If you’ve tried all the inversions and haven’t found a match, try ignoring any 7s in the chord signatures and look again.

When you search through the decoder ring, you could try making a list of close matches: chord signatures that match all of your intervals but have one or more “extra” notes.

Sometimes even the root itself is left out. Check to see if the bass player is playing a note that’s not in the voicing…that may be the root! Add the bass player’s note into your list of intervals and try again.

The second potential issue is that the chord may not be one of the 22 most common chord types! In those cases, the chord’s “correct” name will often be based on one of the common chord types, but with one or more accidentals added on. C7#9 is part of the list, but you can tell from the name that it’s a C7 chord with an added note that’s a #9. You could make a C7#11 by starting with a 7 chord {0,4,7,10} and adding the #11: {0,4,6,7,10}. This is firmly in jazz theory territory, which is beyond the scope of this lesson.

Conclusion

This reverse engineering process might seem complex at first, but with practice, you'll be able to identify most chords in a minute or two. The beauty of this system is that it's completely mechanical—no guesswork required. Once you know the intervals, you can name the chord.

Start by practicing with chord shapes you already know, verifying that the method gives you the right answer. Then branch out to mysterious voicings you find in songbooks or see other players using.