Fretboard Intervals
Same interval, five shapes
Pick an interval and see how its shape changes across each adjacent string pair. Four pairs use one shape — the G→B pair shifts by one fret because the tuning narrows there.
Root note sits on fret 3 of the lower string in each diagram. The offset label above each diagram (+5 frets, +4 frets, etc.) is the distance from the root to the target on the higher string. Notice how G→B is always one fret different from the other four.
What an interval shape is
On guitar, an interval shape is the geometric pattern that produces a given interval between two notes on adjacent strings. A minor 3rd is "down one string, down two frets" — except on the G→B pair, where it's "down one string, down one fret".
These shapes are the building blocks of every chord, arpeggio, and melodic phrase. Once internalised, you can spell any chord on the fly without thinking about note names.
Why this trainer is harder than it looks
The B string. The cursed B string. Five of the six strings are tuned a perfect 4th apart — but G→B is a major 3rd (one semitone narrower). Every interval shape gains one fret on that pair.
The visualizer above shows all five string-pair shapes for any chosen interval side by side. Four pairs look identical; the G→B pair sits one fret over. That's the rule you're memorizing.
The "+1 across G→B" rule, in one table
| Interval | Standard pair offset | G→B pair offset |
|---|---|---|
| m3 | down 1 string, down 2 frets | down 1 string, down 1 fret |
| M3 | down 1 string, down 1 fret | down 1 string, same fret |
| P4 | down 1 string, same fret | down 1 string, +1 fret |
| TT | down 1 string, +1 fret | down 1 string, +2 frets |
| P5 | down 1 string, +2 frets | down 1 string, +3 frets |
| m6 | down 1 string, +3 frets | down 1 string, +4 frets |
| M6 | down 1 string, +4 frets | down 1 string, +5 frets |
| P8 | down 2 strings, +2 frets | down 2 strings, +3 frets |
That single +1 is responsible for 90% of the "why does this chord shape look weird" frustration on guitar.
How interval shapes build chords
A major triad is just root + M3 + P5. Building C major from a root on the A string, fret 3:
- Root: C on the A string, fret 3
- M3: E on the D string, fret 2 — down one string, down one fret
- P5: G on the G string, fret 0 — down one string, down two more frets
Boom — C major is A:3 + D:2 + G:0. Every chord is just a stack of interval shapes. Learn the shapes, build any chord from any root anywhere on the neck.
Shapes lead to "shell voicings"
A "shell voicing" is a chord stripped down to its essential intervals — usually root, 3rd, and 7th. Jazz guitarists use them as harmonic skeletons, then add tensions on top.
- min7 shell: root + m3 + m7
- maj7 shell: root + M3 + M7
- dom7 shell: root + M3 + m7
Build these using interval shapes and you can spell any 7th chord in any key, anywhere on the neck, without ever looking up a chord chart. That's the unlock.