A0 — 27.500 Hz
A0 (A0) is 27.500 Hz in standard equal temperament at A=440 Hz. It is MIDI note number 21.
A0 Frequency in All Tuning Systems
| Temperament | Frequency (Hz) | Cents from Equal | Common Usage |
|---|---|---|---|
| Equal Temperament | 27.500 Hz | 0.00 | Modern standard; piano, fretted instruments |
| Pythagorean Tuning | 27.500 Hz | 0.00 | Medieval/early music; string ensemble open fifths |
| Just / Pure | 27.253 Hz | -15.62 | A cappella vocal, barbershop, Renaissance |
| Meantone 1/3 Comma | 27.500 Hz | 0.00 | Renaissance vocal music in minor keys |
| Meantone 1/4 Comma | 27.500 Hz | 0.00 | Renaissance keyboard, early Baroque organ |
| 1/6 SC - Attenuated | 27.500 Hz | 0.00 | Baroque orchestral ensemble compromise |
| Kellner's Bach | 27.500 Hz | 0.00 | Bach keyboard reconstruction |
| Kirnberger III | 27.500 Hz | 0.00 | Classical-era keyboard, keys near C major |
| Vallotti | 27.500 Hz | 0.00 | Baroque/Classical orchestral tuning |
| Werckmeister III | 27.500 Hz | 0.00 | Baroque keyboard; Bach contemporaries |
| Werckmeister IV | 27.500 Hz | 0.00 | Baroque keyboard, strong key contrast |
| Werckmeister V | 27.500 Hz | 0.00 | Specialized Baroque keyboard |
Positive cents = sharper than equal temperament. Negative cents = flatter. 100 cents = 1 semitone.
A0 at Different Concert Pitches
The same note varies in frequency depending on the concert pitch standard used by your ensemble.
| Concert Pitch | Frequency (Hz) | Common Usage |
|---|---|---|
| A = 440 Hz (ISO standard) | 27.500 Hz | US, UK, and most modern ensembles worldwide |
| A = 442 Hz | 27.625 Hz | Many European orchestras; France, Germany |
| A = 443 Hz | 27.688 Hz | Berlin Philharmonic; some US orchestras |
| A = 432 Hz | 27.000 Hz | Alternative tuning; Baroque revival |
| A = 415 Hz (Baroque) | 25.938 Hz | Historically-informed Baroque performance |
f = f_at_A440 × (concert_pitch / 440)
A0 and the Concert Pitch Standard
The note A in octave 0 is part of the A pitch class — the universal reference for tuning. A4 (440 Hz) is the ISO 16:1975 international standard, but concert pitch has varied across centuries and ensembles.
| Era / Context | A4 Frequency | A0 Frequency | Notes |
|---|---|---|---|
| Baroque (1700s) | 415 Hz | 25.938 Hz | Approximately a semitone lower than modern pitch |
| Classical (late 1700s) | ~422-430 Hz | — | Mozart and Haydn era; pitch was rising but not standardized |
| Alternative standard | 432 Hz | 27.000 Hz | Verdi's preference; popular in alternative tuning communities |
| ISO standard (1975) | 440 Hz | 27.500 Hz | International standard used by most ensembles worldwide |
| European orchestras | 442 Hz | 27.625 Hz | Common in France, Germany, and other European orchestras |
| High modern pitch | 443 Hz | 27.688 Hz | Berlin Philharmonic; some US orchestras |
For any concert pitch standard, A0 = A4_reference × 2-4. A0 is 4 octaves below A4.
Why A0 Varies Across Tuning Systems
A0 shows a maximum deviation of -15.62 cents in Just / Pure compared to equal temperament. This 16-cent difference is clearly audible to trained musicians and reflects how different tuning philosophies prioritize interval purity over equal distribution.
In Just / Pure, A0 is tuned flatter than equal temperament, reflecting this system's approach to distributing the Pythagorean comma across the chromatic scale.
A0 Across All Tuning Systems
Explore how A0 is tuned in each historical temperament system. Each tuning system gives A0 a slightly different frequency, affecting the harmonic character of chords and melodies.
A0 in Historical Temperament Systems
Explore how A0 (27.500 Hz in equal temperament) is tuned in each of the 15 historical non-equal temperament systems. Each system places A0 at a slightly different frequency based on its mathematical basis.
Tune A0 with precision — Get Tunable.
Tunable supports 15+ tuning systems including equal temperament, Pythagorean, just intonation, and historical well-temperaments. See exact Hz values in real-time as you play.
