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7 semitones · pure 3:2

The perfect fifth

Seven semitones, the most stable interval after the octave. Together its two notes blend into one open, hollow sound, the backbone of almost every chord.

A song that starts with a perfect fifth

Going up: Twinkle, Twinkle, Little Star, after its repeated first note ("twin-kle, TWIN"). For a fifth going down there's no famous public-domain tune we'd vouch for: try singing Twinkle's first leap backwards.

The fifth in harmony

Major and minor chords both have a perfect fifth from the root. Tuned pure, 3:2, it's only 2 cents (a cent is a hundredth of a semitone) wider than a piano's, so a fifth sounds right on almost any instrument. A tanpura holds the root and fifth together for exactly that steadiness.

More intervals

Free tools by Stackapella

All of these are free, and so is every course.

Stackapella teaches you to sing harmony one part at a time, right in your browser.

Stackapella recording the alto part of Amazing Grace: each note is a bar with its name, and the one being sung says A little low, go up. Stackapella recording the alto part of Amazing Grace: each note is a bar with its name, and the one being sung says A little low, go up. Stackapella recording the alto part of Amazing Grace: each note is a bar with its name, and the one being sung says A little low, go up. Stackapella recording the alto part of Amazing Grace: each note is a bar with its name, and the one being sung says A little low, go up.
  • A guide sings your partHear your line over the others, slow it down, then take your turn.
  • Your notes light upEach note shows where you landed, and a hint when to go up or down.
  • Record every part yourselfStack your takes in time until you're the whole choir.
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Questions

What is a perfect fifth?

An interval of seven semitones: C to G, or D to A. Its pure ratio is 3:2.

What is the circle of fifths?

The 12 keys in order of fifths: C, G, D, A and so on, each adding a sharp or taking away a flat, until you come back round to C. Neighbouring keys share all but one note.

Why are violins tuned in fifths?

A fifth is easy to tune by ear, because two notes a pure fifth apart stop wobbling when they're right, and four strings in fifths cover a wide range with one hand position.

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Ready to know them by ear? Try interval ear trainingInterval ear training · Name the gap between two notes