Sesquialterum (plural: sesquialtera) or sesquialter refers to the improper rational fraction

.

It is a superparticular number.

The sesquialterum in musical harmony is the ratio corresponding to the interval diapente.

In visual harmony, the sesquialter can be the ratio between the length and width of a rectangle. Most flags of the world's countries have a ratio of 3:2 between their length and width: this ratio is sesquialter. See, for example, the flag of Italy.

In rhythm, the plural sesquialtera refers to a group of three notes which are played in the same time usually occupied by two notes. Sesquialterum is also the ratio between the intervals of time occupied by a dotted note and its corresponding undotted note.

See also: sesquitertium, sesquiquartum, sesquiquintum.

External link

• Manuscript Galileo 72 (Textblock 1 of Folio Page 163v.) (Text in Latin.) The length of bc is twice the length of ab, therefore the ratio of ac to bc is a sesquialterum.