How does the chord finder know which notes belong to a chord?

Every chord type is defined as a set of semitone offsets from the root. A major chord is [0, 4, 7] (root, major 3rd, perfect 5th). The tool adds each offset to the root note index modulo 12 to wrap around the octave, giving the exact pitch class for each chord member.

What is the formula for note frequency?

The standard equal-temperament formula is f = 440 × 2^((n − 69) / 12), where n is the MIDI note number. For example, middle C (C4) is MIDI 60, giving 440 × 2^(−9/12) ≈ 261.6 Hz. Each semitone step multiplies the frequency by the 12th root of 2 (≈1.0595).

What chord types are included?

The tool covers 24 chord types across six categories — Triads (major, minor, diminished, augmented, sus2, sus4), Seventh chords (dominant 7, major 7, minor 7, half-diminished, diminished 7, and more), Sixth chords, Extended chords (9th, 11th, 13th, add9), and Power chords. Enharmonic notes (C# = Db, F# = Gb, etc.) are shown where relevant.

Why does Identify mode sometimes find multiple chord names?

The same set of pitch classes can often be interpreted as more than one chord — for instance, C–E–G–B can be C major 7 (root C) or E minor with added major 7th. This is called enharmonic or reharmonisation ambiguity. The tool lists all valid matches so you can choose the one that fits the harmonic context.

What is a semitone and how do intervals work?

A semitone is the smallest interval in Western equal-temperament tuning — one fret on a guitar, or one adjacent key on a piano. A major 3rd is 4 semitones, a perfect 5th is 7. Chords are built by stacking intervals from a root; a major triad uses intervals [0, 4, 7], while a minor triad uses [0, 3, 7] (flattened 3rd).

Can I use this for guitar, piano, or other instruments?

Yes. The chord finder is instrument-agnostic — it works purely with pitch classes (note names) and frequencies. Once you know the notes in a chord, you can find those pitches on any instrument. The built-in piano keyboard is a visual aid; the note names and intervals apply equally to guitar, bass, ukulele, or any other chromatic instrument.

Chord Finder — Gera Tools

A chord is a group of notes played together to create harmony. Understanding how chords are built — which intervals they use, what each note’s role is, and how they relate to one another — is one of the most practical skills in music, whether you compose, arrange, improvise, or simply want to understand what you are hearing. This tool lets you both build any chord from scratch and identify a chord by clicking its notes.

How it works

Every chord is defined relative to a root note by a list of semitone intervals. A semitone is the smallest step in Western equal-temperament tuning — one piano key, one guitar fret. The major triad uses offsets (0, 4, 7): root, a major 3rd (4 semitones above root), and a perfect 5th (7 semitones above root). Sharpen the 3rd to 4 and you get a major chord; flatten it to 3 and you get a minor chord. Flatten the 5th to 6 and the 3rd stays minor — that is a diminished chord.

For note frequencies, the tool uses the standard equal-temperament formula:

f = 440 × 2^((n − 69) / 12)

where n is the MIDI note number (middle C = 60, A4 = 69 = 440 Hz). Each semitone multiplies the frequency by the 12th root of 2, approximately 1.0595. That means the notes of a C major chord at octave 4 ring at roughly 261.6 Hz (C4), 329.6 Hz (E4), and 392.0 Hz (G4).

In Identify mode the logic is reversed: the tool tests all 12 possible roots against all 24 chord types and returns every combination whose interval set exactly matches the notes you selected — useful when you hear a chord and want to know its name.

Worked example — G dominant 7th

Choose root G and chord type Dominant 7th. The interval offsets are [0, 4, 7, 10]:

Semitones from G	Interval	Note	Freq (oct 4)
0	Root	G	392.0 Hz
4	Major 3rd	B	493.9 Hz
7	Perfect 5th	D	293.7 Hz
10	Minor 7th	F	349.2 Hz

The minor 7th gives G7 its characteristic tension that wants to resolve to C major — the foundation of the dominant-to-tonic motion in Western harmony.

Formula note

All 24 chord types in the library are derived from the same principle: choose a root, apply a fixed set of semitone offsets, and reduce each result modulo 12 to stay within one octave. Extended chords (9th, 11th, 13th) use offsets beyond 12, which the frequency calculator maps to the correct higher octave. Enharmonic spelling (C# vs Db, F# vs Gb) does not change the pitch — both names refer to the same physical frequency; the tool shows the sharp spelling internally and notes the flat equivalent where it exists.