Intervals: Guitar's Secret Decoder Ring

This was the 9th Fret Science YouTube video, released on July 16, 2023. As of December 2025, it has been viewed 378k times, making it my third-most-watched video.

Original video description: Intervals are the building blocks of music, and the guitar fretboard makes them easier to identify and visualize than any other instrument. Learn a simple counting trick that will enable you to identify any interval on the fretboard and then use it to demystify any chord voicing.

Two free tools here put this counting to work: What Chord Is This? names any shape you click in, showing the intervals it counted along the way, and the Chord Name Decoder runs the other direction, spelling out the intervals inside any chord name.

Intervals: guitar’s secret decoder ring

Intervals are the fundamental building blocks of music, and the guitar makes it easier than any other instrument to see and learn them visually. This is the guitar’s superpower.

The major scale is made up of whole-step (two semitone) and half-step (one semitone) intervals. We also call these major seconds and minor seconds.

Intervals are measured in semitones, and there are 12 possible intervals, after which they repeat in the next octave. Since a one-semitone distance is equal to one fret on the guitar, we can lay out all twelve intervals on a single string.

Interval names fall into four groups. The “perfect” intervals include the octave (or P8), the perfect 4th (P4) and perfect 5th (P5). The other intervals from the major scale are called “major” intervals (M2, M3, M6, and M7), and each of those can be flattened to make a “minor” interval (m2, m3, m6, and m7). The last possible interval is the tritone (“tri” for three, and “tone” for whole step). It’s also commonly referred to as a sharp (or augmented) 4, or flat (or diminished) 5.

In some situations you’ll also hear about 9th, 11th, and 13th intervals. These come from extended arpeggios, and they’re used to name chords in jazz, but for fingering purposes, a 9th is exactly the same as a 2nd, an 11th is the same as a 4th, and a 13th is the same as a 6th. Just subtract 7 from the name, and you’ll get a familiar interval.

Intervals can be measured moving either upward or downward in pitch, and it can be helpful to visualize them as arranged in a circle. This also reinforces that there are only 12 possible intervals. Any interval of more than 12 semitones is just a repetition of the same interval one octave (12 semitones) away.

An interval’s complement is the interval that completes the octave. As an example, the complement of a major third (M3) is a minor sixth (m6). Another way of thinking about this is that if you move four semitones (M3), you must move another 8 semitones (m6) to reach a total of twelve semitones, or an octave. Yet another way of thinking about it is that you reach the same note by moving up a major third as you do moving down a minor sixth. In both diagrams on this page, interval complements are visually paired, sharing a single dot.

Only two intervals form their own complements: an octave/unison (12 semitones) and a tritone (6 semitones). For any other interval, we have to specify whether the interval is moving upward or downward. When talking about intervals inside chords, the interval is always named as moving upward from the root note, so Fret Science has adopted the practice of always naming intervals as moving upward from the root unless explicitly stated otherwise.

Because the guitar is mostly tuned in perfect 4ths (5 semitones), it’s easy to measure intervals by counting by fives when we move from string to string, and counting by ones when we move up and down the fretboard. We add five when we move from one string to the next higher string (toward the floor), and we subtract five when we move down to a lower string. We add one when we move one fret toward the bridge, and we subtract one when we move one fret toward the nut. All of this is summarized by this simple diagram and table:

In standard tuning, we have to take special care when we cross between the G and the B strings, because that interval is only a four-fret distance (a major third). The simple solution to this is to count diagonally across this boundary, which I call “the warp”. Here’s an example of doing this for an octave shape (a 12 semitone distance):

The same idea works when we cross “the warp” in the opposite direction. In this case, the interval is minor sixth (8 semitones) moving down:

If you’re measuring a downward interval, you will want to end up with a number between -12 and 0. If you’re measuring an interval moving up, you will want to end up with a number between 0 and 12. If the number you get is outside that range, just add or subtract off twelves until you get an appropriate result. This works because in intervals, extra octaves don’t matter. Once you have the right number, use the table above to map it to an interval name.

This counting trick is especially useful for decoding chord voicings. If you know where the root of the chord is inside the voicing, you can count intervals (upward) to the other notes to determine their harmonic functions within the chord.

For example, we can decode the harmonic functions for the notes in an E7 voicing. The note on the high E string is seven semitones—a perfect fifth—away from the root:

The note on the G string is two semitones down from the root. This is the same note as you’d get by moving ten semitones up, so that note is the minor seventh of the chord:

And the final note is eight semitones down from the root, which is the same as four semitones up, making it a major third:

Here are the most frequently used (and most worthy of memorization) fingerings for each of the 12 intervals in standard tuning. In this chart, I have grouped interval complements together, and all intervals are named as ascending. For example, in the M2/m7 row, the black note is always a major 2nd above the red note, even when the black note falls on a lower string, as it does in column 2. Where applicable, each useful interval is shown both straddling and not straddling “the warp”. In these diagrams, the “shorter” interval is from red to black, and the longer interval is from black to red.