Key signature calculator

What the result means

The result lists accidentals in conventional order and names a major key and its relative minor. A signature is a set of accidentals that normally applies to every matching note in the passage, unless a local accidental overrides it. Positive settings add sharps, negative settings add flats, and zero means no sharps or flats, which corresponds to C major and A minor. The calculator keeps spellings such as C-flat major and A-sharp minor when the signature calls for them, so the output is a notation fact rather than a simplified pitch list.

Why it helps reading

Reading a key signature quickly saves effort at every note. Once you know which accidentals are in force, you can read a staff without re-checking each note against the key. Knowing the relative major and minor helps you guess the tonic from the signature, though it does not confirm the key by itself. Tonic emphasis, cadences and harmony are needed to decide which key the music actually uses. Treat the calculator as a fast reference for the signature, not as a full analysis of the piece.

Limits to keep in mind

A signature alone does not determine whether a passage is in its major or its relative minor. Local accidentals, a tonic chord that resolves in one key and not the other, and harmonic context still matter. A three-sharp signature could belong to A major or to F-sharp minor, and only the music will tell you which. The calculator does not analyze audio, does not play sound, and does not track your progress over time.

Try it step by step

1. Set the signature field to 0, then predict the accidentals before changing the count. Confirm the result shows no sharps or flats and names C major with A minor.
2. Set the field to 3 and read the listed accidentals: F-sharp, C-sharp and G-sharp. Name the major key (A major) and relative minor (F-sharp minor) without changing the field.
3. Set the field to 4 and compare it with 3. Identify only the newly added accidental, which is D-sharp, and check that it is the sharp that follows G-sharp in the sharp order.
4. Set the field to -3 and read the flats: B-flat, E-flat and A-flat. Name the major key (E-flat major) and relative minor (C minor). Then, at a physical piano or in an external notation app, play or write a C natural minor scale and check that it uses the same three flats.

A concrete example

At 0 the pair is C major and A minor. At +3, F#, C# and G# give A major and F# minor. At +4, adding D# gives E major and C# minor. A relative-minor tonic is three semitones below its major tonic: A down to F#, or E down to C#.

A common wrong turn

Assuming the key is always the major key named by the signature, so a piece with three sharps is always read as A major even when its final chord and melody center on F-sharp.

Try this instead: Treat the signature as a pair of possibilities. Look at the opening and closing tonic, the bass line and the cadences to decide between the major key and its relative minor. Name the candidate tonic first, then confirm it with the harmony.

Where to go next — and why