There is a simple way to remember the key signature of a given key or to find a closely-related key (that is, one that has a similar key signature). Instead of thinking of octaves as a continuously repeating pattern going off into infinity in both directions, think of an octave as a closed circle that keeps bringing you back to your starting point.

Circle of Fifths

Sharp Keys Now use this circle to count off intervals of a perfect fifth. Start at C, because C major has no sharps or flats. First we'll go in the sharp direction (on this circle, clockwise). The key of C major has no sharps or flats. The key a perfect fifth (seven half steps) higher than C major - G major - has one sharp, F sharp. The key a perfect fifth higher than G major - D major - has two sharps. It keeps the F sharp, and adds C sharp, which is a perfect fifth higher than F sharp (although written a perfect fourth lower, in order to stay on the staff). This pattern continues; each leap up a perfect fifth gives a key that keeps all the previous sharps and adds one more sharp that is a perfect fifth (P5) higher than the last sharp added (or a perfect fourth(P4) lower; since key affects all octaves, P5 higher and P4 lower are essentially the same thing here). You can continue indefinitely around the circle in perfect-fifth jumps; this rule will always hold up. For example, if you continue until you find yourself at B sharp, you will be at the same spot on the circle as C major. At that point, in B sharp you would have added twelve sharps (many of the notes would be double sharps), probably not a key you would want to write or read in, but if you played the scale it would sound exactly like a C major scale. The circle of fifths works just as well for minor keys, but you would start counting at A minor, since that is the minor key with no sharps and flats.

Every seven half steps, or perfect fifth, in the clockwise direction gives you a key with one more sharp. Here is an animation showing counting on the circle of fifths in the sharp direction. After D major, name the next four sharp keys, and name the sharp that is added with each key. A major adds G sharp E major adds D sharp B major adds A sharp F sharp major adds E sharp

E minor is the first sharp minor key; the first sharp added in both major and minor keys is always F sharp. Name the next three sharp minor keys, and the sharp that is added in each key. B minor adds C sharp F sharp minor adds G sharp C sharp minor adds D sharp

Flat Keys Now let's go in the flat direction (here, counterclockwise). The key a perfect fifth lower than C major is F major, which has one flat, B flat. Go down another perfect fifth from F major; the key of B flat has two flats, B flat and E flat. E flat is a perfect fifth lower, or a perfect fourth higher, than B flat.

Moving around the circle seven half steps (a perfect fifth) in the counterclockwise direction gives a key with one more flat. After B flat major, name the next four flat keys, and name the flat that is added with each key. E flat major adds A flat A flat major adds D flat D flat major adds G flat G flat major adds C flat

And, of course, if you continue to go around the circle in the flat direction, eventually you would arrive at D double flat major, which would be difficult to read but would sound exactly the same as C major. In the last example, you may have noticed yet another pattern that can be helpful in remembering which key goes with which key signature. Given a flat key signature, you can name the major key by naming the second-to-last flat in the key signature. The rule for naming sharp major keys is to name the note a half step higher than the last sharp. The minor key will always be the relative minor, a minor third lower than the major key.

The last sharp is D sharp. The key is E major, a half step higher than D sharp. The relative minor is C sharp minor.

The second-to-last flat is E flat. The key is E flat major. The relative minor is C minor. Name the major and minor keys for each key signature.

D major or B minor; B major or G sharp minor; B flat major or G minor; G flat major or E flat minor.

Related Keys Related keys are keys with similar key signatures. The keys most closely related to a given key have only one flat or sharp more or less than the given key. The relative minor or major of any key is also considered closely related, since it has the same key signature. The key of D major has two sharps. Using the circle of fifths, we find that the most closely related major keys (one in each direction) are G major, with only one sharp, and A major, with three sharps. The relative minors of all of these keys (B minor, E minor, and F sharp minor) are also closely related to D major. What are the keys most closely related to E flat major? To A minor? E flat major (3 flats): B flat major (2 flats) A flat major (4 flats) C minor (3 flats) G minor (2 flats) F minor (4 flats) A minor (no sharps or flats): E minor (1 sharp) D minor (1 flat) C major (no sharps or flats) G major (1 sharp) F major (1 flat)