Music theory basics · updated 2026-08-16

EQUAL TEMPERAMENT

The tuning system that splits the octave into twelve equal semitones so every key sounds usable, at the cost of pure intervals.

Music theory basics — Photograph of a printed score of Mozart's Rondo alla Turca open on a music desk, showing staves, key signature and note heads — the written notation this section defines.

Key takeaways

The tuning system that splits the octave into twelve equal semitones so every key sounds usable, at the cost of pure intervals.
It is the compromise that makes modulation and fixed-pitch instruments practical, and it is what every DAW, tuner and synth defaults to.
The equal-tempered major third is about fourteen cents sharp of the pure ratio, which is why sustained thirds on a piano beat slightly against a vocal.
Watch out: assuming equal temperament is universal.
Sits under music theory basics in this glossary, with 2 primary sources below.

Quick checklist

Can you define equal temperament in one sentence without looking?
Can you point at equal temperament in a real session, mix or contract?
Have you tried the practical move above at least once?
Would you catch the common mistake before it costs you a take?
Have you opened one of the primary sources below rather than a forum thread?

EQUAL TEMPERAMENT IN DEPTH

Twelve-tone equal temperament divides the octave into twelve identical semitones so every key sounds equally in tune — and equally slightly out. It is the compromise that makes modulation and fixed-pitch instruments practical, and it is what every DAW, tuner and synth defaults to.

How it works in practice

The equal-tempered major third is about fourteen cents sharp of the pure ratio, which is why sustained thirds on a piano beat slightly against a vocal.

The mistake people make

Assuming equal temperament is universal. Much of the world's music, and a growing amount of experimental electronic work, uses other tunings; most modern synths accept alternate tuning tables.

WHERE EQUAL TEMPERAMENT SITS

Equal temperament belongs to music theory basics in the Sampled music glossary. The vocabulary you need before anyone can explain a chart, a chord chart, or a session to you.

TERMS THAT DEPEND ON EQUAL TEMPERAMENT

Semitone and whole tone
The semitone is the smallest step in Western equal temperament; two semitones make a whole tone. Everything from scales to chord spelling is counted in them.

TEST YOURSELF

0/3 answered · 0 correct

3 quick questions on equal temperament. Answers are marked instantly — nothing is sent anywhere.

1. Which statement best describes equal temperament?
2. What is the mistake people most often make with equal temperament?
3. In practice, which of these applies to equal temperament?

Ready for the full thing? Take the 25-question terminology test and get a certificate with your name and score.

SOURCES AND CITATIONS

Free, primary references for equal temperament — standards bodies, manufacturers, government offices and university course material. Each one lists the line of this entry it backs up.

Stanford CCRMA — tuning and intervals (opens in a new tab)
University research centre · Stanford CCRMA
“The tuning system that splits the octave into twelve equal semitones so every key sounds usable, at the cost of pure intervals.”— the claim this source supports
Why it counts: The CCRMA course material derives this from first principles, so you can check the maths behind the plain-English version above.
Open Music Theory (opens in a new tab)
Open textbook · Open Music Theory
“Twelve-tone equal temperament divides the octave into twelve identical semitones so every key sounds equally in tune — and equally slightly out.”— the claim this source supports
Why it counts: An openly licensed university textbook, so the definition can be checked against a citable academic source.

RELATED TERMS IN MUSIC THEORY BASICS

Back to the full music glossary or read our latest articles.