Musical Frequencies
C4
261.63 Hz
Note: C4
Cosmic Octave Color
Derived visible color (521 nm)
Display swatch #44c55f
EstablishedMusical Standard
Evidence Level
Established
Source Count
1
Last Reviewed
March 23, 2026
Directly measured, standardized, or well-supported in mainstream scientific or technical literature.
This entry documents a musical reference or standard. It should be read as an acoustic and musical reference rather than a biological claim.
Review the evidence modelMusical note C in octave 4. Mid to treble range.
Period
3.82 ms
Wavelength
1.31 m
Nearest Note
C4 (0¢)
Claim Type
Musical Standard
Cosmic Octave Color
Derived visible color (521 nm) · #44c55f
Source
Equal temperament tuning system (A4 = 440 Hz)
Sources
Equal Temperament Tuning System
108 atlas references
The twelve-tone equal temperament reference used for note-frequency lookups throughout the atlas.
Standard equal-temperament note table with A4 = 440 Hz.
Harmonic Series
musicequal-temperamentoctave-4