Cent (music)

The cent is a logarithmic measure of relative pitch or intervals. 1200 cents are equal to one octave, and an equally tempered semitone is equal to 100 cents. The formula to determine the value in cents between two notes with frequencies a and b is:

The measure was developed by A. J. Ellis around the 1870s, and was published in his edition of Hermann von Helmholtz's On the Sensations of Tone. It has since become the standard way of measuring intervals.