Chord Lab — Chord Construction Calculator & Studio
Type any chord symbol — Cmaj7, F#m7b5, Bb13, G7#9, Am9 — and Chord Lab builds it from music theory: correctly spelled notes, interval formula, every inversion, piano diagram, playable guitar voicings, audio playback and the exact frequency of each tone. Six studio tools in one page, 101 chord qualities, zero servers.
Chord construction lab
Enter a chord symbol. Understands sharps/flats (F#, Bb), unicode (Cø, C°7, CΔ7), extensions (13, #11, b9), sus/add qualities and slash chords (C/E).
Reverse chord finder (exact match)
Type the notes you hear or play, separated by spaces — e.g. C E G Bb — and the lab names every chord in its 101-quality database with exactly those pitch classes.
Type notes separated by spaces, e.g. "C E G Bb".
Chord tone & note frequencies
Equal temperament: f = 440 × 2((n−69)/12), where n is the MIDI note number (A4 = 69). Middle C (C4, MIDI 60) = 261.63 Hz.
Chromatic reference
Transpose chords
Move a chord by semitones with correct enharmonic respelling — E up a major 2nd becomes F#, never Gb; C up a minor 3rd becomes Eb. Slash-chord bass notes transpose too.
Capo calculator
The chord you finger (shape) plus the capo fret = the chord that sounds. C shape + capo 3 sounds Eb.
Capo position finder
Want to play in a hard key using easy open shapes? Enter the shape's root and the target key.
Transposing instrument converter
Written pitch ⇄ concert pitch. A Bb trumpet sounds a major 2nd below written; Eb alto sax a major 6th below; F horn a perfect 5th below.
Reference: common transposing instruments
| Instrument | Key | Sounds … below written | Written C5 sounds |
|---|---|---|---|
| Bb trumpet, clarinet, soprano & tenor sax | Bb | major 2nd (2 semitones) | Bb4 |
| Eb alto & baritone sax | Eb | major 6th (9 semitones) | Eb4 |
| F horn, English horn | F | perfect 5th (7 semitones) | F4 |
| Piccolo | C (8va) | — (sounds octave above) | C6 |
Chord progression builder
Diatonic chords for any key. Click any chord to open it in the Chord Lab.
Common progressions
Fret position calculator
From the nut, fret n sits at scale_length × (1 − 2−n/12). The 12th fret is exactly half the scale length.
Common scale lengths: Fender 25.5″ (648 mm), Gibson 24.75″ (629 mm), PRS 25″ (635 mm), bass 34″ (864 mm).
What you can do with Chord Lab
- Chord spelling calculator: type any symbol and get every note spelled from its interval degree — D7♯9 yields E♯, never F.
- Chord voicing calculator: every inversion gets three ranked guitar voicings (canonical open shapes first) plus a piano diagram.
- Chord frequency calculator: each chord tone listed with MIDI number and exact Hz via f = 440 × 2((n−69)/12).
- Chord identifier from notes: the reverse finder names exact pitch-class matches from the 101-quality database.
- Jazz chord vocabulary: extended chords (9ths, 11ths, 13ths), 7th chord qualities and altered dominants (♭9, ♯9, ♯11, ♭13, alt) with correct spellings.
- Ukulele & other instruments: note spelling, frequencies, transposition and progressions are instrument-independent and work for ukulele, bass or keys players; fretboard diagrams are drawn for 6-string guitar.
How chord construction works
Every chord is a stack of intervals above its root. Cmaj7 = root (C) + major 3rd (E) + perfect 5th (G) + major 7th (B), formula 1–3–5–7. Flatten the 3rd and 7th and you get Cm7 (C–Eb–G–Bb, 1–♭3–5–♭7). Extend to the 9th, 11th and 13th for jazz colors: C13 stacks 1–3–5–♭7–9–11–13.
The hard part — and the reason this lab exists — is spelling. Pitch classes alone are not enough: D7♯9 contains E♯, not F, because the ♯9 must be spelled as a kind of E (the 9th degree). The lab derives every note name from its interval degree, so F♯m7♭5 correctly yields F♯–A–C–E and G♭7 yields G♭–B♭–D♭–F♭.
Chord database: 101 qualities
Every quality below is spelled from its interval formula and verified note-by-note. Click a quality to build it on C in the lab.
101 chord qualities, each spelled from its interval formula. Click any chip to build it in the lab.
Major family (14)
Minor family (12)
Dominant family (28)
Diminished / augmented / suspended (16)
Extended & altered dominants (31)
Methodology & formulas
- Note frequency: f = 440 × 2((n−69)/12) Hz (equal temperament, A4 = 440 Hz ISO 16).
- Transpose: pitch classes move modulo 12; spelling follows the transposed interval (E + major 2nd = F♯; C + minor 3rd = E♭).
- Capo: sounding chord = shape transposed up by the capo fret (semitones).
- Transposing instruments: concert = written − offset (B♭: 2, E♭: 9, F: 7 semitones).
- Fret position: d(n) = L × (1 − 2−n/12) from the nut.
- Guitar voicings: deterministic search over 4-fret windows in the chosen tuning; ranks root-bass voicings with complete chord tones, playable spans and clear bass strings first. Canonical open shapes (x32010, xx0232, 022000) rank first by construction.
Chord Lab vs other chord tools
| Chord Lab (this page) | scales-chords.com | cmuse.org capo chart | |
|---|---|---|---|
| Chord construction (name → notes) | ✅ 101 qualities, spelled | ✅ | — |
| Reverse chord namer (notes → name) | ⚠️ exact matches only | ✅ deep recursive naming | — |
| Inversions with voicings | ✅ all positions + guitar shapes | partial | — |
| Note frequencies per chord tone | ✅ MIDI + Hz | — | — |
| Capo: shape → sounding chord | ✅ any fret, any shape | — | ✅ static chart |
| Transpose ± semitones | ✅ | — | — |
| Transposing instruments | ✅ B♭/E♭/F | — | — |
| Progression builder (12 keys) | ✅ | — | partial (Nashville) |
| Fret position calculator | ✅ any scale length | — | — |
| Audio playback (Web Audio) | ✅ chord/strum/voicing | — | — |
| Privacy (client-side only) | ✅ zero requests | ? | ? |
Comparison is about feature coverage for the listed tasks, checked October 2026. scales-chords.com remains the deeper reverse namer — use it when the lab reports no exact match.
Frequently asked questions
How do you spell a Cmaj7 chord?
Cmaj7 is spelled C – E – G – B: root, major 3rd, perfect 5th, major 7th (formula 1–3–5–7). Type any chord symbol into the Chord Lab above — for example F#m7b5 or Bb13 — and it shows the correctly spelled notes, the interval formula, all inversions, piano and guitar voicings, and the frequency of every tone.
What notes are in an F#m7b5 chord?
F#m7b5 (F# half-diminished) is spelled F# – A – C – E: root, minor 3rd, diminished 5th, minor 7th. Note the spelling uses C natural for the flat fifth, not B# — the lab spells every chord tone from its interval degree, so enharmonics are always musically correct (D7#9 gives you E#, not F).
How do chord inversions work?
An inversion keeps the same notes but puts a different chord tone in the bass. Cmaj7 (C–E–G–B) has four positions: root position (C in bass), 1st inversion (E in bass), 2nd inversion (G in bass) and 3rd inversion (B in bass). Triads have three positions; seventh chords have four. Select any inversion in the Chord Lab to see its bass note, piano diagram and playable guitar voicing.
How do you calculate the frequency of a musical note?
Use equal-temperament formula f = 440 × 2^((n − 69) / 12), where n is the MIDI note number (A4 = 69). Middle C (C4, MIDI 60) is 440 × 2^(−9/12) = 261.63 Hz. The Frequencies tab computes this for any note and lists every chord tone with its MIDI number and Hz.
Why is A4 tuned to 440 Hz?
A4 = 440 Hz is the ISO 16 international standard pitch adopted in 1975 (and used as the de-facto orchestral reference since 1939). Some ensembles use 442 Hz and Baroque music often uses 415 Hz, but 440 Hz is the default reference for tuners, sample libraries and this calculator.
How does a capo transpose chords?
A capo raises every string by the same number of semitones, so the chord you finger (the shape) sounds higher by the capo position: actual chord = shape transposed up by the capo fret. A C shape with capo 3 sounds Eb; a G shape with capo 2 sounds A. Enter your shape and capo fret in the Capo tab — or ask which capo position lets you play a target key with easy open shapes.
How do I transpose chords up 2 semitones?
Move every chord tone — including the bass of slash chords — up by 2 semitones and respell: G becomes A, Am becomes Bm, C/E becomes D/F#. The Transpose tool does this for any interval (−11 to +11 semitones) and keeps correct enharmonic spelling automatically.
What is a transposing instrument?
On a transposing instrument the written note differs from the concert (sounding) pitch by a fixed interval. A Bb trumpet sounds a major 2nd below its written pitch: written C5 sounds Bb4. An Eb alto sax sounds a major 6th below written (written C5 sounds Eb4), and an F horn sounds a perfect 5th below (written C5 sounds F4). The Instruments tab converts in both directions.
How do I transpose concert-pitch music for Eb alto sax?
Write it a major 6th (9 semitones) higher than concert pitch: concert C4 becomes written A4 for the alto sax. For Bb trumpet, write a major 2nd higher (concert C4 → written D4). Select the instrument and direction in the Instruments tab and convert note by note.
What chords are in the key of G major?
The diatonic triads in G major are G (I), Am (ii), Bm (iii), C (IV), D (V), Em (vi) and F#dim (vii°). Toggle sevenths to get Gmaj7, Am7, Bm7, Cmaj7, D7, Em7 and F#m7b5. The Progressions tab builds this for all 12 keys, major and minor.
What is the I–V–vi–IV progression in the key of C?
In C major, I–V–vi–IV is C – G – Am – F — the famous four-chord progression behind hundreds of pop songs. Pick any key in the Progressions tab and it spells eight common progressions (doo-wop I–vi–IV–V, jazz ii–V–I–vi, Andalusian i–VII–VI–V in minor, and more) with one click.
How are guitar fret positions calculated?
The distance of fret n from the nut is scale_length × (1 − 2^(−n/12)). On a 25.5-inch scale the 12th fret sits at exactly 12.75 inches — half the scale length, the octave. The old luthier 'rule of 18' (divide the remaining length by 17.817 per fret) is an approximation of the same math. The Fret Positions tab tables every fret for any scale length.
What is the difference between a chord finder and a chord calculator?
A chord finder (reverse lookup) names the chord from notes you give it — that is the specialty of sites like scales-chords.com. A chord calculator / construction lab works the other way: you type a chord name and it builds the chord — notes, intervals, inversions, voicings and frequencies. This lab focuses on construction (101 chord qualities), capo/transpose math and progressions; its reverse namer handles exact matches honestly rather than pretending to out-name the specialists.
When do I write F# and when Gb?
F# and Gb are enharmonic — same pitch, different spelling. The correct choice comes from key and interval context: the raised 4th in G major is F#, the minor 3rd of Eb minor is Gb. The lab spells chord tones from their interval degree (never by pitch-class lookup), so D7#9 correctly gives E# rather than F, and transposition preserves interval spelling (E up a major 2nd is F#, not Gb).
Is my data sent anywhere? Is this private?
No. Chord Lab runs 100% in your browser: chord symbols you type, notes you play and every calculation stay on your device. The page makes zero network requests after loading — there is no account, no tracking and nothing to sign up for. Audio playback is synthesized locally with the Web Audio API.
Is Chord Lab free? Do I need an account?
Completely free, no account, no signup, no download. It is a single self-contained web page that works offline once loaded, built by nrtechstudio.com.