The alto recorder in F, also known as a treble (and, historically, as consort flute and common flute) is a member of the recorder family.

The alto is between the soprano and tenor in size, and is correspondingly intermediate in pitch. It has the same general shape as a soprano, but is approximately 50% larger in all dimensions. A 50% increase in length causes a 50% increase in the wavelength for a given fingering. This lowers the pitch by a perfect fifth, that is from C to F. 

The F alto is a non-transposing instrument, although its basic scale is in F, that is, a fifth lower than the soprano recorder and a fourth higher than the tenor (both with a basic scale in C). So-called F fingerings are therefore used, as with the bassoon or the low register of the clarinet, in contrast to the C fingerings used for most other woodwinds. Its notation is usually at sounding pitch, but sometimes is written an octave lower than it sounds.