# C (musical note)
**C** is one of the seven letter names used in Western music to designate a pitch class, the set of all pitches that sound an octave-related frequency. In twelve-tone equal temperament tuned to the A440 standard, middle C sounds at approximately 261.63 Hz, and the note serves as a central reference point for keyboards, octave numbering, and the key of [C major](https://www.edgepedia.org/c-major).[1](https://graphsearch.epfl.ch/en/concept/49220)
| Key fact | Detail |
|---|---|
| Frequency of middle C | About 261.63 Hz in equal temperament with A4 = 440 Hz, a standard widely adopted in 1939[1](https://graphsearch.epfl.ch/en/concept/49220) |
| Designations | C4 in scientific pitch notation, c in Helmholtz pitch notation, note number 60 in MIDI[1](https://graphsearch.epfl.ch/en/concept/49220) |
| Keyboard position | The fourth C key from the left on a standard 88-key piano[1](https://graphsearch.epfl.ch/en/concept/49220) |
| Pitch standard | ISO 16:1975 fixes the reference at the note A in the treble stave, 440 Hz, from which C's frequency follows[2](https://www.iso.org/es/contents/data/standard/00/36/3601.html) |
| Octave rule | Every octave slice of the keyboard starts on a C; the B just below middle C belongs to the octave below and is called B3[3](https://www.grammarofmusic.com/en/topics/octave-designation) |
| Solfège name | Do in fixed do systems, where do is always C[4](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/) |
| C major scale | C, D, E, F, G, A, B[5](https://www.musicradar.com/guitars/they-describe-themselves-as-a-mantra-rock-dada-pythago-cubist-orchestra-and-the-band-name-translates-to-angina-of-the-chest-the-microtonal-music-theory-behind-viral-math-rockers-angine-de-poitrine) |
## Frequency and pitch standards
The frequency of a written C is not fixed by the letter name itself. Under the A440 pitch standard, in which the A above middle C is tuned to 440 Hz, middle C sounds at about 261.63 Hz in twelve-tone equal temperament.[1](https://graphsearch.epfl.ch/en/concept/49220) The international standard ISO 16:1975 specifies the standard tuning frequency as the note A in the treble stave, set at 440 Hz, with tuning and retuning to be effected by instruments producing it within an accuracy of 0.5 Hz.[2](https://www.iso.org/es/contents/data/standard/00/36/3601.html) Because the standard defines A rather than C, the value of C is derived from the tuning system: equal temperament uses a constant semitone frequency ratio of \( 2^{1/12} \), and C4 sits nine semitones below A4.[6](https://arxiv.org/abs/1508.02292)
The exact value of middle C also depends on the temperament in use. Taking A4 to be 440 Hz, the frequency of middle C is 261.63 Hz under equal temperament, 263.40 Hz under Werckmeister III, and 263.18 Hz under quarter-comma meantone.[7](https://piano.org/tools/temperament-calculator/)
The same letter can correspond to different sounding frequencies in practice. A C can be realized musically in many different frequencies depending on the musical context, for example when playing a transposing instrument, on which a written C produces a different concert pitch.[8](https://www.researchgate.net/profile/Tellef-Kvifte/publication/270819567_Instruments_and_the_Electronic_Age_Toward_a_Terminology_for_a_Unified_Description_of_Playing_Technique/links/5a61cc4eaca272a158176afa/Instruments-and-the-Electronic-Age-Toward-a-Terminology-for-a-Unified-Description-of-Playing-Technique.pdf) Two notes an octave apart carry the same letter name, with the upper one vibrating at twice the rate of the lower one; whichever C is performed or vocalized, the pitch remains identical, and the frequency follows a power-of-two relationship.[9](https://openstax.org/books/contemporary-mathematics/pages/13-4-math-and-music)
## Octave designation
Because a concert grand piano has eight keys all called C, a bare letter name is ambiguous off the staff, and octave numbering exists to say which C is meant.[3](https://www.grammarofmusic.com/en/topics/octave-designation) All common systems rest on a single structural choice: the keyboard is divided into octave-wide segments, each beginning on a C and finishing on the following B, and each note within a segment takes that segment's number.[3](https://www.grammarofmusic.com/en/topics/octave-designation)
In scientific pitch notation, also called USA Standard, the lowest organ C is C0 and middle C is C4; the octave above starts on C5 and the one below on C3.[3](https://www.grammarofmusic.com/en/topics/octave-designation) The rule for finding a note's number is that it takes the number of the nearest C below it, so the D just above middle C is D4 and the tuning A is A4, while the B just below middle C is B3.[3](https://www.grammarofmusic.com/en/topics/octave-designation) The number follows the letter, not the sound: B sharp sounds like C but stays in B's octave, and C flat sounds like B but stays in C's octave.[3](https://www.grammarofmusic.com/en/topics/octave-designation)
**Competing systems.** [Scientific pitch notation](https://www.edgepedia.org/scientific-pitch-notation) is not the only scheme in circulation. The theorist Lacerda numbers the Cs from 1 to 9, making middle C dó 5, and Med divides the range of musical sounds into eight octaves from the lowest, making middle C dó 3 with the two lowest octaves numbered −2 and −1.[3](https://www.grammarofmusic.com/en/topics/octave-designation) Each system is internally consistent, and reading a pitch designation correctly depends on knowing which convention is in use.[3](https://www.grammarofmusic.com/en/topics/octave-designation)
## Naming systems for C
The letter C belongs to the A-to-G letter system used in English-speaking countries and most software, in which sharps and flats are written with the letter plus a symbol, as in C sharp or B flat.[4](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/) In fixed do solfège, standard across the Romance-language world including Spanish, Italian, French, and Portuguese, the syllable do is always C; la is A at 440 Hz permanently.[4](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/) This differs from the movable do taught to many English speakers, where do is whatever the tonic of the current key happens to be.[4](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/)
Across German-speaking countries and much of central and northern Europe, a variant letter system is used in which what English speakers call B natural is notated as H, while B denotes B flat instead; the squared form of the letter gradually came to be written as an h in German manuscripts, and that name endured.[4](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/) C itself is written the same way in all of these systems.
## Historical role in notation
The note C has carried structural weight in Western staff notation since its beginnings. In the earliest staff notation, the count of lines was inconsistent, possibly beginning with just two, one marking F and the other C, and a letter placed at the beginning of each staff indicated whether that line represented C or F, or occasionally B flat.[10](https://ugc.futurelearn.com/uploads/files/c8/d8/c8d8a472-8e29-46c9-ac70-a29b1bb627ba/History-of-Notation1_Tim_Morris.pdf) A stylized letter C, G, or F placed at the beginning of the staff on one of the lines establishes a point of reference from which the locations of the other notes on the staff can be determined; this symbol is the clef.[11](https://academics.hamilton.edu/music/spellman/class_notes/notation.html) The letter C appears as the clef in the manuscript of the medieval song "[Sumer is icumen in](https://www.edgepedia.org/sumer-is-icumen-in)," next to the flat symbol for B flat.[12](https://themusicstudio.ca/the-evolution-of-musical-notation/)
## C in music theory
C is the tonic of the C major scale, which consists of the notes C, D, E, F, G, A, and B.[5](https://www.musicradar.com/guitars/they-describe-themselves-as-a-mantra-rock-dada-pythago-cubist-orchestra-and-the-band-name-translates-to-angina-of-the-chest-the-microtonal-music-theory-behind-viral-math-rockers-angine-de-poitrine) Because this scale uses the seven letter names with no sharps or flats, C major is often the first key presented in instruction, and the octave beginning on C lists the twelve chromatic notes as C, C sharp, D, D sharp, E, F, F sharp, G, G sharp, A, A sharp, and B.[9](https://openstax.org/books/contemporary-mathematics/pages/13-4-math-and-music) Middle C also functions as a practical dividing point between the treble and bass staves, and its fixed designation C4 makes it a common anchor for describing the ranges of instruments and voices.[1](https://graphsearch.epfl.ch/en/concept/49220)
## References
1. [C (musical note), EPFL Graph Search](https://graphsearch.epfl.ch/en/concept/49220)
2. [ISO 16:1975, Acoustics — Standard tuning frequency (Standard musical pitch), International Organization for Standardization](https://www.iso.org/es/contents/data/standard/00/36/3601.html)
3. [Octave designation, Grammar of Music](https://www.grammarofmusic.com/en/topics/octave-designation)
4. [Note names around the world, TuneHaven](https://tunehaven.bytehavenstudios.com/docs/note-naming-systems/)
5. [The microtonal music theory behind Angine de Poitrine, MusicRadar](https://www.musicradar.com/guitars/they-describe-themselves-as-a-mantra-rock-dada-pythago-cubist-orchestra-and-the-band-name-translates-to-angina-of-the-chest-the-microtonal-music-theory-behind-viral-math-rockers-angine-de-poitrine)
6. [Revising the Musical Equal Temperament, arXiv](https://arxiv.org/abs/1508.02292)
7. [Temperament Calculator: Hz and Cents Tables, Piano Technicians Guild](https://piano.org/tools/temperament-calculator/)
8. [Tellef Kvifte, Instruments and the Electronic Age: Toward a Terminology for a Unified Description of Playing Technique](https://www.researchgate.net/profile/Tellef-Kvifte/publication/270819567_Instruments_and_the_Electronic_Age_Toward_a_Terminology_for_a_Unified_Description_of_Playing_Technique/links/5a61cc4eaca272a158176afa/Instruments-and-the-Electronic-Age-Toward-a-Terminology-for-a-Unified-Description-of-Playing-Technique.pdf)
9. [13.4 Math and Music, Contemporary Mathematics, OpenStax](https://openstax.org/books/contemporary-mathematics/pages/13-4-math-and-music)
10. [Music notation — a short history, ABRSM Teacher Development (Tim Morris)](https://ugc.futurelearn.com/uploads/files/c8/d8/c8d8a472-8e29-46c9-ac70-a29b1bb627ba/History-of-Notation1_Tim_Morris.pdf)
11. [A Brief History of Musical Notation, Hamilton College](https://academics.hamilton.edu/music/spellman/class_notes/notation.html)
12. [The Evolution of Musical Notation, The Music Studio](https://themusicstudio.ca/the-evolution-of-musical-notation/)
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*Topic: Encyclopedia › Arts and culture › Music › Musical practice and theory › Instruments, theory, and world traditions › Pitch, tuning, scales, and musical acoustics*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 25, 2026 · Edited: Sep 30, 2026; Oct 25, 2026 · Last review: Oct 25, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license