Music Theory

What Is A Key Signature In Music: A Beginner’s Guide

Written by Dan Farrant

Last updated

When it comes to music theory, key signatures are an essential part of making music easier to read. They also allow us to know which accidentals we should use and what key we’re playing in.

In this guide, I’m going to cover everything you need to know about key signatures and how they’re used. But first, what is a key?

What is a Key in Music?

If a piece of music uses notes from one particular scale, then we’d say it is in that ‘key.’ 

For example, if a piece of music uses only notes in G major scale, then it would be in the key of G major. Or, if a piece of music uses only notes in F major scale, then it would be in the key of F major, etc.

The example below is in the key of G major, as it uses only the notes from that scale.

Without a key signature

Recommended Reading

For more info, check out our guide to what a key in music is here.

What is a Key Signature?

When writing out music in a certain key, we’d have to write in a sharp or flat every time that note came up. If you were to do this in some keys, then it can mean adding in a lot of accidentals, and the music can get very cluttered.

However, to save us from having to add all the sharps or flats each, and whenever we’re playing in a given key, we use a key signature at the beginning of the music to make it easier to read.

For example, here is that same melody but using a key signature.

With a key signature

Instead of writing a sharp in front of every single F, we write one at the beginning, which then tells the musician to play an F# every time—even the F in the first space of the stave.

If the piece was in D major, it would have an F sharp (F#) and a C sharp (C#) as its key signature because D major has two sharps. 

For example, this piece in D major without a key signature:

Example of a piece in D major without a key signature

But with a key signature, it becomes this:

Example of a piece in D major with a key signature

Another example of a piece in F major without a key signature:

Example of a piece in F major without a key signature

But with a key signature, it looks like this:

Example of a piece in F major with a key signature

A piece in C major obviously doesn’t have any sharps or flats in its key signature as there aren’t any black notes in C major scale.

Where Does The Key Signature Go?

The key signature is always written after the clef but before the time signature.

It’s important not to write it after the time signature as this is a common mistake beginners make.

The Order of Key Signatures

When writing key signatures, you can’t choose any old order of the accidentals. There are a few rules that you have to follow.

The first rule is that you can only use either sharps or flats. Never both.

It’s important always to put the key signature in the right place. 

For example, in the treble clef, F sharp (F#) is always on the 5th line of the stave, but in the bass clef, it’s on the 4th line.

Here are the three key signatures in both clefs.

G major key signature
D major key signature
F major key signature

Hopefully, that helps you make a bit more sense of key signatures. I’ll be adding to this post soon, going over the other key signatures plus the different clefs like the alto and tenor clef.

In the meantime, I recommend making some flashcards to help you memorize them.

Photo of author

Dan Farrant, the founder of Hello Music Theory, has been teaching music for over 15 years, helping hundreds of thousands of students unlock the joy of music. He graduated from The Royal Academy of Music in 2012 and then launched Hello Music Theory in 2014. He plays the guitar, piano, bass guitar and double bass and loves teaching music theory.