Lucky for you beginning piano players, there’s a method to the madness of key signatures, an order that starts with no sharps and flats and cycles the ring of keys to all twelve keys. Check out the famous Circle of Fifths with the letter names for each possible home key, or tonal center.
As you travel around the circle, you find each of the twelve keys in the Western tonal system. The numbers inside the circle tell you how many sharps or flats are in each key signature.
As you check out the Circle of Fifths, note the following important points:
Each key is a fifth up from the previous key, circling clockwise.
The key of C, at the top, has no sharps or flats.
The keys on the right half of the Circle are all sharp keys, gaining one sharp at each position traveling clockwise from the top.
The keys on the left half of the Circle are all flat keys, gaining one flat at each position traveling counterclockwise from the top.
The three keys at the bottom of the circle can be either sharp or flat keys; the composer gets to decide.
Among the marvels of this oracle of tonality, the Circle shows the relationship of the keys to each other. The keys that are neighbors have a lot in common, like seven of eight scale tones. Very often a song travels smoothly to a neighboring key during its musical journey.
The keys that are farthest away from each other have little in common, and a musical journey from one side of the Circle directly to the opposite side sounds quite abrupt.
The order of sharps and flats as they’re written on the grand staff follows the Circle of Fifths, adding a sharp or flat in the same order as the Circle.
Key signatures with sharps
Suppose you want to play a song on the piano that has two sharps in the key signature. If you look at the Circle of Fifths, you can quickly see that the key with two sharps is two positions away from C, so the song is in the key of D.
Eventually you want to be able to know what key a song is in without glancing at the Circle. Here’s how.
To read a key signature that contains sharps:
Locate the last sharp (the one farthest to the right) on either the treble or bass clef.
Move up one half step from the sharp to find the name of the key.
For example, if you have two sharps, F sharp and C sharp, the last one on the clef is C sharp. Up a half step from C sharp is D. Therefore, the song is in the key of D.
Naming keys with lots of sharps requires a bit of brain power because note spelling can get tricky. For example, on your piano keyboard the key one half step up from E is F. Technically, you can also spell F as E sharp. So, if the sixth sharp in the key signature is E sharp, you raise it one half step to determine the correct key, which is F sharp.
You can’t determine the key to be G flat because you would be skipping the letter name F in the sequence of note names.
Key signatures with flats
To read a key signature that contains flats:
Locate the next-to-the-last flat (the one that’s second from the right) in the key signature.
The name of that flat is the name of the key.
For example, if you have three flats in a key signature — B flat, E flat, and A flat — the next-to-last one is E flat, and so the song is in the key of E flat.
The one key for which this naming method doesn’t work is the key of F. Because it has only one flat (B flat), there’s no such thing as a “next-to-the-last” flat for you to read. But all you have to do is remember that one flat in the key signature means that a song is in the key of F.
You can also remember that F is the key with one flat because it’s one position before the key of C in the Circle of Fifths, or a fifth below C, so it must have one flat.