A4 — 440.000 Hz
A4 (A4) is 440.000 Hz in standard equal temperament at A=440 Hz. It is MIDI note number 69.
A4 Frequency in All Tuning Systems
| Temperament | Frequency (Hz) | Cents from Equal | Common Usage |
|---|---|---|---|
| Equal Temperament | 440.000 Hz | 0.00 | Modern standard; piano, fretted instruments |
| Pythagorean | 440.000 Hz | 0.00 | Medieval/early music; string ensemble open fifths |
| Just Intonation (Major) | 436.043 Hz | -15.64 | A cappella vocal, barbershop, Renaissance |
| Just Intonation (Minor) | 436.043 Hz | -15.64 | Minor-key vocal music, string ensembles |
| Quarter-Comma Meantone | 440.000 Hz | 0.00 | Renaissance keyboard, early Baroque organ |
| Third-Comma Meantone | 440.000 Hz | 0.00 | Renaissance vocal music in minor keys |
| Sixth-Comma Meantone | 440.000 Hz | 0.00 | Baroque orchestral ensemble compromise |
| Werckmeister III | 440.000 Hz | 0.00 | Baroque keyboard; Bach contemporaries |
| Werckmeister IV | 440.000 Hz | 0.00 | Baroque keyboard, strong key contrast |
| Werckmeister V | 440.000 Hz | 0.00 | Specialized Baroque keyboard |
| Kirnberger III | 440.000 Hz | 0.00 | Classical-era keyboard, keys near C major |
| Vallotti | 440.000 Hz | 0.00 | Baroque/Classical orchestral tuning |
| Young (1799) | 440.000 Hz | 0.00 | Classical-era keyboard |
| Bach/Lehman | 440.000 Hz | 0.00 | Bach keyboard works, Well-Tempered Clavier |
| Neidhardt | 440.000 Hz | 0.00 | 18th century keyboard, near-equal alternative |
| Kellner (Bach) | 440.000 Hz | 0.00 | Bach keyboard reconstruction |
Positive cents = sharper than equal temperament. Negative cents = flatter. 100 cents = 1 semitone.
A4 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) | 440.000 Hz | US, UK, and most modern ensembles worldwide |
| A = 442 Hz | 442.000 Hz | Many European orchestras; France, Germany |
| A = 443 Hz | 443.000 Hz | Berlin Philharmonic; some US orchestras |
| A = 432 Hz | 432.000 Hz | Alternative tuning; Baroque revival |
| A = 415 Hz (Baroque) | 415.000 Hz | Historically-informed Baroque performance |
f = f_at_A440 × (concert_pitch / 440)
Instruments That Play A4
A4 (440.000 Hz) falls within the comfortable playing range of 46 instruments.
A4 and the Concert Pitch Standard
The note A in octave 4 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 | A4 Frequency | Notes |
|---|---|---|---|
| Baroque (1700s) | 415 Hz | 415.000 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 | 432.000 Hz | Verdi's preference; popular in alternative tuning communities |
| ISO standard (1975) | 440 Hz | 440.000 Hz | International standard used by most ensembles worldwide |
| European orchestras | 442 Hz | 442.000 Hz | Common in France, Germany, and other European orchestras |
| High modern pitch | 443 Hz | 443.000 Hz | Berlin Philharmonic; some US orchestras |
For any concert pitch standard, A4 = A4_reference × 20. A4 equals the reference pitch directly.
Why A4 Varies Across Tuning Systems
A4 shows a maximum deviation of -15.64 cents in Just Intonation (Major) 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 Intonation (Major), A4 is tuned flatter than equal temperament, reflecting this system's approach to distributing the Pythagorean comma across the chromatic scale.
2 of the 15 non-equal temperaments deviate by more than 10 cents for A4, making this note one where tuning system choice has a meaningful impact on pitch.
A4 Across All Tuning Systems
Explore how A4 is tuned in each historical temperament system. Each tuning system gives A4 a slightly different frequency, affecting the harmonic character of chords and melodies.
A4 as the Tuning Reference — Historical Temperament Systems
A4 = 440 Hz is the universal tuning reference. In each historical temperament, A4 itself remains 440 Hz — but the surrounding chromatic notes are tuned differently according to the system's mathematical basis. Explore A4 as the anchor pitch for each of the 15 non-equal temperament systems:
Tune A4 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.