Circle of Fifths / Key Signature Calculator
Pick a key and see its key signature — how many sharps or flats and exactly which notes are altered (G major has 1 sharp, F♯; D major has F♯ and C♯; F major has 1 flat, B♭) — along with its scale, its relative major/minor, and its place on the circle of fifths. The circle arranges the 12 keys by perfect fifth (each step clockwise adds a sharp, each step counter-clockwise adds a flat), so adjacent keys share 6 of 7 notes and are "closely related"; enharmonic pairs like F♯/G♭ sit opposite C. Sharps accumulate in the order F♯–C♯–G♯–D♯–A♯–E♯–B♯ and flats in B♭–E♭–A♭–D♭–G♭–C♭–F♭. Everything runs locally in your browser.
Circle of fifths
Key signature
Scale
All major & minor key signatures
The math. A key's signature comes from walking the circle of fifths from C: each perfect fifth up (7 semitones, C→G→D→A→E→B→F♯→C♯) adds one sharp, and each fifth down (C→F→B♭→E♭→A♭→D♭→G♭→C♭) adds one flat. The sharps accumulate in the order F♯, C♯, G♯, D♯, A♯, E♯, B♯ (the cycle of fifths starting from F), and the flats in the reverse order B♭, E♭, A♭, D♭, G♭, C♭, F♭ — so a key with n sharps alters the first n notes of that sharp order, and likewise for flats. The relative minor of a major key sits a minor third (3 semitones) below it and shares the same signature (C major ↔ A minor, G major ↔ E minor); the relative major is a minor third above the minor key. The 7-note diatonic scale spells out the 7 letters A–G in order from the tonic, with the signature's accidentals applied. Enharmonic keys (F♯ major = G♭ major, both 6 accidentals) sound identical in 12-tone equal temperament but are spelled differently for notation. Pairs with the Scale Generator (notes of any scale or mode) and the Note Frequency Calculator. Everything runs locally — nothing leaves your browser.