In this guide
A key signature is a group of sharps or flats written near the beginning of a staff. It shows which note letters are normally altered throughout the music. A major key and its relative minor share a signature, so use the musical context to identify the key.
For the tonal idea behind the notation, see what a key in music means.
New to note patterns? Learn what a scale in music is with major and minor examples.
A key signature is a set of sharps or flats written near the beginning of a musical staff. It tells a reader which note letters are normally raised or lowered throughout the music, unless a later accidental or key-signature change indicates otherwise.
For example, a signature containing one sharp marks F as F-sharp. That applies to F notes in all octaves, not only the position of the printed symbol. The same signature is commonly used for G major and E minor, so the signature alone does not always tell you which key the piece is in.
How to read a key signature
- Find the clef. The signature appears after the clef at the beginning of a staff, before the time signature when one is present. It is normally repeated after the clef at the start of each system.
- Identify the marked note letters. Sharps raise their note letters by a semitone; flats lower them by a semitone. A signature normally contains sharps or flats, not a mixture of both.
- Apply the signature while reading. If the signature has B-flat, written B notes are normally played as B-flat in every octave. A later accidental can temporarily alter a note according to notation conventions.
- Look at the musical context. Identify likely tonic notes and chords, phrase endings and accidentals. A major key and its relative minor share the same signature, and music can also be modal or change key.
The University of Puget Sound’s major-key signature guide shows the notation and ordering of sharps and flats. A key signature is a reading aid, not a rule that forbids notes outside a scale.
Examples of key signatures
| Signature | Notes normally altered | Common relative keys |
|---|---|---|
| No sharps or flats | None in the signature. | C major or A minor. |
| One sharp | F-sharp. | G major or E minor. |
| Two sharps | F-sharp and C-sharp. | D major or B minor. |
| One flat | B-flat. | F major or D minor. |
| Two flats | B-flat and E-flat. | B-flat major or G minor. |
These are common major/minor interpretations, not the only possible tonal contexts. For example, a piece using a mode can share a signature while centering on a different note. Individual accidentals can also appear within a section.
Key signature vs. musical key vs. scale
| Term | Meaning | Example |
|---|---|---|
| Key signature | Notation showing recurring sharps or flats on a staff. | One sharp indicates F-sharp by default. |
| Musical key | A tonal context organized around a tonic, commonly described as major or minor. | G major has G as its tonic. |
| Scale | An ordered set of pitches described by a pattern of intervals. | G major: G, A, B, C, D, E and F-sharp. |
In E natural minor, the notes E, F-sharp, G, A, B, C and D use the same pitch set as G major, but E rather than G is the tonic. Musical emphasis, chords and phrase endings help distinguish them. Minor-key music can also use altered notes outside the natural-minor collection. Berklee’s guide to modes discusses tonic and scale type as parts of describing a tonal context.
What about accidentals and key changes?
An accidental written before a note can change that note from the signature’s default. In standard notation, its effect generally lasts through the measure for the same pitch and octave, subject to conventions such as ties. A natural sign can cancel a sharp or flat in the relevant context. Notation practices vary, so check the score and its editorial conventions.
A piece can also change key. A new key signature may be written at a section change, but not every temporary change of tonal center receives a new signature. Repeated accidentals and harmonic context can provide clues; the University of Puget Sound’s modulation guide gives examples of those clues.
How to check the key of a recording
- Listen for a tonal center. Choose a representative passage and notice which note or chord feels like a point of rest. A short loop or an unresolved section can be ambiguous.
- Compare candidates. Consider the relative major and minor, and check the bass, melody and phrase endings. A shared pitch collection does not settle which tonic is central.
- Use an estimate as a starting point. The song key finder analyzes supported short mono or stereo MP3/WAV audio locally and returns candidates. It does not read a score, identify every key change or guarantee the correct key.
- Verify by ear and context. Try the candidate tonic against several sections, then compare an alternative. For a detailed listening workflow, see how to find a song’s key by ear.
Changing a key
Transposition moves notes by a consistent interval. If an entire C-major passage is shifted up two semitones, its tonic becomes D and its major relationships remain the same. A fixed shift does not turn a major passage into minor.
The audio pitch changer can shift a supported short audio file by a selected interval; it does not detect the starting key or edit a printed key signature. Listen to the export for artifacts, and see how to change a song’s key for the full workflow.
Common questions
Does no key signature always mean C major?
No. It can also be used for A minor and other contexts. Determine the tonal center from the music rather than the signature alone.
Is a key signature the same as a time signature?
No. A key signature shows default sharps or flats in notation. A time signature describes how beats or note values are organized; see time signatures explained.
Does a key signature mean no other notes can be used?
No. Accidentals and chromatic notes can appear, and music can move temporarily or permanently to another tonal center.