A minor third () is the smaller of two commonly occurring musical intervals compounded of two steps of the diatonic scale. The prefix 'minor' identifies it as being the smaller of the two (by one semitone); its larger counterpart being a major third. The minor third is abbreviated as m3 and its inversion is the major sixth.

The minor scale is so named because of the presence of this interval between its tonic and mediant (1st and 3rd) scale degrees. Minor chords too, take their name from the presence of this interval built on the chord's root (provided that the interval of a perfect fifth from the root is also present or implied).

A minor third in just intonation corresponds to a pitch ratio of 6:5 (). In an equal tempered tuning, a minor third is equal to three semitones, a ratio of 1:2^3/12 (approximately 1:1.189), or 300 cents, 15.641 cents smaller. In other meantone tunings it is larger, and in 19 equal temperament it is very nearly the 6:5 ratio of just intonation.

Other pitch ratios are given related names, the septimal minor third with ratio 7:6 and the tridecimal minor third with ratio 13:11 in particular.

The minor third is classed as an imperfect consonance and is considered one of the most consonant intervals after the unison, octave, perfect fifth, and perfect fourth.

Instruments in A are a minor 3rd lower than the written pitch in the concert pitch, i.e. how they are heard. Therefore, to get the written pitch, transpose the concert pitch up a minor 3rd.

See also

• musical tuning
• semiditono
• List of meantone intervals

et:Väike terts it:Terza minore lt:Ma?oji tercija no:Liten ters