Key Signatures: How Keys Work in Music

The key signature is your roadmap to the harmonic and melodic context of a piece of music.

You need to know key signatures to play along with other musicians or record on top of tracks in your DAW session.

But remembering your key signatures is hard if you don’t know how. And seeing them written can be confusing when you’re not used to it.

Even so, knowing your key signatures isn’t too difficult once you understand how they work.

In this article I’ll explain key signatures and show the easiest way to identify them in a piece and remember them on your instrument.

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What is a key signature?

A key signature is the collection of sharps and flats that determines the key of a piece of music. The key is the group of pitches that makes up the main major or minor scale that will be used in the composition. The key signature appears at the beginning of a line of music to indicate which notes must be altered from their original state to fit the key.

How to identify the key signature

To situate yourself on your instrument when you play music from a score, you have to identify its key.

To situate yourself on your instrument when you play music from a score, you have to identify its key.

Luckily, identifying the key signature of a written piece of music is easy. All you have to do is analyze the pattern of sharps and flats in a specific way.

Here’s how to find the key of any piece of written music:

• For keys with sharps—the last sharp in the key signature is the leading tone or 7th scale degree of the key. Count up one semitone to get to the tonic.
• For keys with flats—the second to last flat is the root of the key. Simple as that!

If you’ve been following closely, you may have realized a problem. How can you tell if the key is major and not the relative minor that shares the same key signature?

Getting this right is slightly more complicated. It involves doing a little harmonic analysis to be 100% sure.

But here’s a big hint: songs typically begin and end on tonic harmony. For the majority of songs, the first note in the lowest voice is the root of the key.

For the majority of songs, the first note in the lowest voice is the root of the key.

In a major key you can use the trick of counting from the last sharp or second to last flat. But if you find that the first note isn’t what you expect, you may be looking at a minor key.

Here’s how to confirm the key:

• Listen to the song if possible. If the harmony rests and feels most stable on minor harmony, it’s probably in minor!
• Look for harmony that moves from dominant to tonic at the end of a phrase. A strong cadence is a sure sign that confirms the key.

Circle of fifths: the order of sharps and flats

Music accidentals are written in a specific order in a key signature.

That order will be familiar to anyone who knows the circle of fifths. But don’t worry if you don’t.

There are two handy mnemonics for remembering the order of sharps and flats:

• For keys with sharps, the rhyme goes: Father Charles Goes Down And Ends Battle
• For keys with flats, the rhyme goes: Battle Ends And Down Goes Charles Father

You can remember this by saying the rhyme in your head as you write the key signature at the beginning of the line.

If you know your intervals well you can also just count up by fifths for sharp keys and down by fourths for flat keys.

How to remember any key signature

But what if you’re just improvising music on your instrument to find an idea?

If you’re trying to remember the notes that need to be altered to fit the key, you can use the circle of fifths to find the key signature.

Here’s the trick:

Remember that the circle of fifths begins with C major, which contains no sharps or flats.

From there, each step you take on the circle of fifths by following the order in the rhyme adds another sharp to the key signature.

Then you simply add that number of sharps to the key signature following the pattern.

Here’s a chart to simplify the sharp keys for you:

For flat keys, the pattern follows the order of flats rhyme starting again from C major. Here’s the chart:

Enharmonic keys

You may have noticed that some spellings of some keys are absent on this chart. What if you’re trying to play in G# major!?

The reason is that some keys can be represented more simply using their enharmonic equivalents.

Enharmonic tones are notes that can be written using two different spellings.

Enharmonic tones are notes that can be written using two different spellings.

If you lower an A note by one semitone it becomes Ab. And if you raise a G note by one semitone it becomes G#.

These are two different ways to represent the same pitch class.

So if G# and Ab are the same, why is Ab better?

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If you write try to write the key signature of G# so that it follows the tone-semitone pattern of the major scale, something curious happens.

To preserve the semitone interval between the leading tone and the tonic you would have to use…F double sharp.

Of course, raising F by two semitones is enharmonically equivalent to G. That’s why it’s much simpler to think of this key as Ab major!

Get it in key

Knowing key signatures is an important skill to develop as a musician.

If you know where you are at all times on your instrument you’ll be able to play and write freely—that’s a huge benefit for creativity.

Use the tips and tricks in this guide to never forget key signatures again.

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Michael Hahn is an engineer and producer at Autoland and member of the swirling indie rock trio Slight.

@Michael Hahn