Key Signatures and How to Read Them

Quick Tricks to Learn the Key to Play

Key signature in E-major and c-sharp-minor
Artur Jan Fijałkowskipl Wikimedia Commons

When you are about to play a song and you are looking at a piece of sheet music it would help to know what key you need to play in. To find out, look at the very beginning of the music, on the musical staff, right after the clef, you may see a set of flats or sharps. That is the key signature. Just like a written signature tells you the name of a person, a key signature tells you the key to playing the music.

The key signature is written immediately before the time signature.

Reason for a Key Signature

The purpose of the key signature, aside from telling you what key to play in, is to avoid writing too many accidentals, like sharps and flats, throughout the sheet music. 

For example, if a song is written in B flat, then that means throughout the song, in most cases, when you see a B in the sheet music, then you will need to play a B flat. A song that is written in B flat likely has a lot of Bs in the sheet music. So, instead of writing a flat repeatedly on all the Bs in the song, the flat sign, which looks similar to a "b" sign, is placed on the third line of the treble clef at the beginning of the song indicating that the Bs need to be flatted. If you know the key signature at the beginning, then you can plan ahead while playing the song. 

Some instruments may play up or down through the octaves, in that case, the key signature tells you that all the other notes of the same letter, even if they are in other octaves, need to be sharped or flatted.

The easiest key signature to know or remember is C major, which has no sharps or flats in its key signature. 

Sometimes, composers change the key signature throughout a piece of music. When this happens, it is usually after a double barline in the sheet music.

Fast Way to Know the Key to Play

There are a few fast tricks of the trade to learn what key you need to play in.

You can determine the key you are playing in by looking at the sharps or flats and apply a little trick. Or, you can memorize the number of flats or sharps and automatically know what key you are playing in.

Keep in mind that there are only seven flats: B-E-A-D-G-C-F and the flats always appear in the same order in a key signature. On the other hand, the order of sharps: F-C-G-D-A-E-B always appears in the same order. If you note, the order of sharps is actually the same order of the flats (B-E-A-D-G-C-F), but backward.

Quick Tricks With the Major Key (Sharps)

If the key signature has sharps, look at the position of the last sharp and raise it by a half-step to get the key. For example, if the last sharp is E, raise it a half step which is F, the key is F sharp major.

You can also count the sharps and know what key you are playing in.

Number of SharpsKey Signature
0 sharpsC
1 sharpG
2 sharpsD
3 sharpsA
4 sharpsE
5 sharpsB
6 sharpsF sharp
7 sharpsC sharp

Quick Tricks With the Major Key (Flats)

When the key signature has flats, simply look at the second to the last flat and you get the key. So, for example, if A flat is the second to the last flat in the key signature, this means the music is in A flat major.

The exceptions are F major because it only has one flat and C major because it has no flats or sharps.

Number of SharpsKey Signature
0 flatsC
1 flatF
2 flatsB flat
3 flatsE flat
4 flatsA flat
5 flatsD flat
6 flatsG flat
7 flatsC flat

Quick Trick With the Minor Key

Simply find the name of the key in major and lower it three half steps to get the minor key. For example, E flat major lowered three half steps will be C minor. A minor key that has the same key signature as a major key is called a relative minor. For example E flat major and C minor both have 3 flats but C minor is three half steps lower than E flat major.

For another quick reference, you can memorize or keep a table of key signatures handy for both major and minor keys.