Interval ratio

Ratios, rather than direct frequency measurements, allow musicians to work with relative pitch measurements applicable to many instruments in an intuitive manner, whereas one rarely has the frequencies of fixed pitched instruments memorized and rarely has the capabilities to measure the changes of adjustable pitch instruments (electronic tuner).

Frequency ratios are used to describe intervals in both Western and non-Western music.

When a musical instrument is tuned using a just intonation tuning system, the size of the main intervals can be expressed by small-integer ratios, such as 1:1 (unison), 2:1 (octave), 3:2 (perfect fifth), 4:3 (perfect fourth), 5:4 (major third), 6:5 (minor third).

To most people, just intervals sound consonant, i.e. pleasant and well-tuned.

For instance, an equal tempered perfect fifth has a frequency ratio of about 1.4983:1 (or 14983:10000).