Key Signatures Explained: Sharps, Flats and How to Read Them
By Solfa Theory · Published: 24 October 2026 · Updated: 24 October 2026
Quick answer: what is a key signature?
A key signature is the set of sharps or flats printed at the start of every staff (UK: stave) line. It tells you which notes are raised or lowered for the whole piece, and it also tells you the likely key. To read it, find the last sharp and go up a semitone, or for flats use the second-to-last flat.
Why key signatures exist
Imagine a song in D major. It uses F sharp and C sharp every time those notes appear. Writing a sharp sign next to each one would clutter the page. Instead, the two sharps are written once at the beginning, and every F and C in the piece is played sharp unless told otherwise.
That is all a key signature is: a time-saving shorthand. It also gives you a quick hint about which key you are in, which is why learning to read it is one of the best early skills in reading sheet music.
Sharps, flats and naturals
A sharp raises a note by one semitone (US: half step). A flat lowers it by one semitone. A natural cancels a sharp or flat. These signs are the same whether they sit in a key signature or next to a single note. For a closer look at the signs themselves, see the Wikipedia page on accidentals.
The order of sharps and flats
Sharps and flats always appear in the same order, so a key signature looks the same on every score. According to Wikipedia's article on key signatures, the order of sharps is F, C, G, D, A, E, B, and the order of flats is B, E, A, D, G, C, F. The flat order is simply the sharp order reversed.
A common memory aid for sharps is "Father Charles Goes Down And Ends Battle". Say it backwards for flats: "Battle Ends And Down Goes Charles's Father".
How to find the key from the key signature
There are two quick rules.
- Sharps: find the last sharp, then go up one semitone. That note is the name of the major key. Three sharps (F, C, G): the last is G sharp, one semitone above is A, so the key is A major.
- Flats: with two or more flats, the second-to-last flat names the key. Three flats (B, E, A): the second-to-last is E, so the key is E flat major. One flat is the exception: it is always F major.
No sharps or flats means C major. If you learn only one thing, learn that every key signature has exactly one major and one minor reading.
All the major keys at a glance
| Sharps or flats | Major key | Relative minor |
|---|---|---|
| None | C | A minor |
| 1 sharp | G | E minor |
| 2 sharps | D | B minor |
| 3 sharps | A | F sharp minor |
| 4 sharps | E | C sharp minor |
| 5 sharps | B | G sharp minor |
| 6 sharps | F sharp | D sharp minor |
| 1 flat | F | D minor |
| 2 flats | B flat | G minor |
| 3 flats | E flat | C minor |
| 4 flats | A flat | F minor |
| 5 flats | D flat | B flat minor |
| 6 flats | G flat | E flat minor |
F sharp major (6 sharps) and G flat major (6 flats) are enharmonic: they sound the same and are written differently. The same pattern is laid out as a wheel in our circle of fifths guide.
Major or minor? Relative keys
Each key signature belongs to a pair of keys. A minor key starts a minor third (3 semitones) below its relative major, so A minor shares the key signature of C major, and E minor shares G major's one sharp. To decide which one a piece is in, listen for the note that feels like home. Look at the final chord too, since pieces usually end on it. For more on how the two moods differ, read major vs minor scales.
Key signature vs accidental
A key signature covers the whole piece. An accidental is a one-off sharp, flat or natural beside a single note. As the accidentals article explains, an accidental lasts until the end of the bar (US: measure) it appears in, unless another accidental changes the note again. If you see an accidental that is not in the key signature, the music is borrowing a note from outside the key, which is common in melodies and chord changes.
How to practise
- Write out the order of sharps and flats from memory each day for a week.
- Pick a random key signature and name the major key and its relative minor.
- Play the scale on the online piano or the scale explorer to hear that those sharps or flats are what make the scale sound right.
- Combine it with the 15-minute daily practice routine.
Frequently asked questions
What is a key signature?
A key signature is the group of sharps or flats written at the start of each staff line. It tells you which notes are raised or lowered throughout the piece, so you do not have to mark them every time they appear.
How do you find the key from a key signature with sharps?
Look at the last sharp, then go up one semitone (half step). If the last sharp is C sharp, the key is D major. The key signature with no sharps or flats is C major (or A minor).
How do you find the key from a key signature with flats?
With two or more flats, the key is named after the second-to-last flat. With four flats (B, E, A, D), the key is A flat major. With a single flat, the key is F major.
What is the difference between a key signature and an accidental?
A key signature applies to the whole piece or section. An accidental is a sharp, flat or natural placed next to a single note, and it normally lasts only until the end of that bar (US: measure).
How many sharps and flats can a key signature have?
Up to seven. Seven sharps gives C sharp major and seven flats gives C flat major. Keys with that many are rare in practice, since an enharmonic key with fewer sharps or flats is usually easier to read.
Does the key signature tell you if a piece is major or minor?
Not by itself. Every key signature fits one major key and one minor key, called relative keys. You decide between them by listening for the home note and checking where the music settles.
Where to go next
Once key signatures feel natural, use them to find the key of a song, then build the chords of your key with triads explained. If you are new to all of this, start with music theory for beginners.