How to Read Key Signatures

By: Jerry A. Greene

Question: I am a returning piano student (playing the piano again for the first time in 20 years). I have been playing again for almost a year. I guess I could be considered Low Intermediate as a pianist. My question is this: How, when playing a piece/song, can you tell what key it is in?

Answer: Figuring out what key you're in can be done in a few different ways. Assuming that you don't have a "Circle-of-Fifth's" diagram in front of you, lets look at it this way:

First, figure out if the key is in major, or minor. (Generally the sound of the piece should tell you...Major is generally a "happy" sound, Minor is generally a "sad", or "mad" sound.

From any major scale, we can figure out the relative minor (which shares the same key signature). The 6th degree of the major scale is the tone that starts the relative minor.

Examples are below:

No Sharps, or Flats

If the key signature has no sharps, or flats, you are in the key of C Major, or C's relative minor: A Minor. (6th Scale Degree of C)

Sharp Key Signatures

If there are sharps, look at the LAST sharp (reading left to right) and go up a 1/2 step. The letter you come up with is your Major Key, and again, the 6th degree of THAT scale gives you the relative minor which shares the same key signature.

Example: 3 Sharps ... F# C# G# ... G# is the last sharp, so go up a half step from there ... You come up with A ... A Major is the name of the key (or F# Minor)

Flat Key Signatures

If there are flats, look at the second to last flat (from left to right) and whatever the last flat is, is the name of the key.

Example: 2 Flats ... Bb Eb ... Bb is the second to last flat and is hence the name of the key (Bb Major, or G Minor)

This works for all Flat keys except the one with only 1 Flat (since there is no second to last flat (from left to right)). The name of this key is F Major (or D Minor, it's relative):


There are different "modes" that share the same key signature, but this should help you for 99% of what you play.