Chromatic scale drawn as a circle: each note is equidistant from its neighbors, separated by a semitone of the same size.
The chromatic scale is a musical scale with twelve pitches, each a semitone above or below another. On a modern piano or other equal-tempered instrument, all the semitones are the same size (100 cents). In other words, the notes of an equal-tempered chromatic scale are equally spaced. An equal-tempered chromatic scale is a nondiatonic scale having no tonic because of the symmetry of its equally spaced notes.1
The most common conception of the chromatic scale before the 13th century was the Pythagorean chromatic scale. Due to a different tuning technique, the twelve semitones in this scale have two slightly different sizes. Thus, the scale is not perfectly symmetric. Many other tuning systems, developed in the ensuing centuries, share a similar asymmetry. Equally spaced pitches are provided only by equal temperament tuning systems, which are widely used in contemporary music.
The term chromatic derives from the Greek word chroma, meaning color. Chromatic notes are traditionally understood as harmonically inessential embellishments, shadings, or inflections of diatonic notes.
The chromatic scale has no set spelling agreed upon by all. Its spelling is, however, often dependent upon major or minor key signatures and whether the scale is ascending or descending. The images above, therefore, are only examples of chromatic scale notations. As an abstract theoretical entity (that is, outside a particular musical context), the chromatic scale is usually notated such that no scale degree is used more than twice in succession (for instance G flat - G natural - G sharp).
The ancient Chinese chromatic scale is called Shí-èr-lǜ. However, "it should not be imagined that this gamut ever functioned as a scale, and it is erroneous to refer to the 'Chinese chromatic scale', as some Western writers have done. The series of twelve notes known as the twelve lü were simply a series of fundamental notes from which scales could be constructed."2
The Indiansolfège, i.e. sargam, makes up the twelve notes of the chromatic scale with respective sharps and flats.