The Double-Sharp in Music Notation

Double-sharps on the staff.
A Cx and Gx on the staff means you'll play a D and A natural, respectively.

Brandy Kraemer

A double-sharp is an accidental for a note that has two sharps, meaning the original note is raised by two half-steps (also called semitones). The double-sharp symbol resembles a bold letter "x" and is placed before a notehead, similar to other accidentals.

The primary difference between a single sharp and a double sharp is the number of half-steps by which the natural note is altered. With a regular sharp, the natural note is raised one half-step, whereas, with a double-sharp, the natural note is raised two half-steps — meaning it is raised by a whole step. 

On the piano, single sharps usually point to black piano keys; double-sharps often point to piano naturals. For example, G# is a black key, but Gx is otherwise known as A-natural. You can read more about enharmonic notes to understand when one note has two different names, and why they are used in music notation. Exceptions to the concept of double-sharps resulting in a white key are Bx and Ex, which are the C# and F# keys.

The Purpose of the Double-Sharp

Double-accidentals are not seen in any working key signature. In fact, if there were a key signature after C# major (which has the maximum of seven sharps), it would contain one F double-sharp, but that idea really belongs to a conversation about theoretical key signatures.

In everyday notation, double-sharps are necessary for certain scenarios. In its essence, the double-sharp is largely used for purposes of adhering to the rules of music theory. For example, a piece of music written in the key of C# Major puts a sharp on every note. Let's say that the composer wanted to write an A natural in a measure that already contains some A#s. Instead of alternating between writing A natural and A# sharp the composer might indicate the harmony on an A natural with a G double-sharp. In another instance, the rule also applies to chords. A chord typically has a root, a third, a fifth, and in this example, a seventh. The intervals indicate their place above the root of the chord. In an A# major 7th chord, there are four notes. The root, A#; the major third, Cx; the perfect fifth, E#; and the major seventh, which is Gx. 

Canceling a Double-Sharp

A double-sharp is canceled in a couple of different ways. First, it depends if the note should revert back to a regularly sharped note or back to its natural state. For reverting a double-sharped note back to a single-sharp, simply indicate the change by placing a sharp symbol in front of the notehead. It is also considered correct to indicate a natural sign and a sharp sign in front of the notehead, but it tends to be more difficult to read. However, if the note needs to be returned back to its completely natural state, a natural sign would be used.

Other Names for a Double-Sharp

Musical terms can have different identities in other common music languages such as Italian, French, and German. In Italian, the double-sharp is called a doppio diesis; in French, it's a double-dièse; and in German, it is a Doppelkreuz.