What is the exact frequency of musical note C#3?

In 12-Tone Equal Temperament (12-TET) with concert pitch A4 = 440 Hz (ISO 16:1975), the exact acoustic frequency of C#3 is 138.59 Hz.

What is the acoustic wavelength of C#3 in air?

At standard room temperature (20°C / 68°F) where sound travels at 343.21 m/s, the acoustic wavelength of C#3 is approximately 247.64 cm (2.48 meters).

What is the piano key and MIDI number for C#3?

C#3 corresponds to piano key number 29 on a standard 88-key keyboard, and MIDI note number 49.

How is the frequency of C#3 calculated?

It is calculated using the formula f = 440 · 2^((k - 49)/12), where k is the piano key number (29) and 49 represents A4 (440 Hz).

Acoustics & Musical Physics Labf = 440 · 2^((k-49)/12) • λ = v / f

C#3 (138.59 Hz) Note to Frequency Calculator

Discover the acoustic frequency, wavelength in air, MIDI number, and physical tuning mathematics for musical note C#3.

12-Tone Equal Temperament Pitch

C#3(Key #29, MIDI 49)

Frequency

138.59 Hz

Wavelength (Air @ 20°C)

2.48 m

Period (T = 1/f)

7.22 ms

Interactive 88-Key Piano KeyboardScroll or click keys to navigate

A0 #

C1 #

D1 #

F1 #

G1 #

A1 #

C2 #

D2 #

F2 #

G2 #

A2 #

C3 #

D3 #

F3 #

G3 #

A3 #

C4 #

D4 #

F4 #

G4 #

A4 #

C5 #

D5 #

F5 #

G5 #

A5 #

C6 #

D6 #

F6 #

G6 #

A6 #

C7 #

D7 #

F7 #

G7 #

A7 #

The Physics of Note C#3 (138.59 Hz)

When C#3 is played on a piano or acoustic instrument, vibrating strings or air columns compress adjacent atmospheric molecules at a fundamental frequency of 138.59 cycles per second (Hz). In standard air at 20°C, each compression wavefront is separated by 247.64 cm.

12-Tone Equal Temperament (12-TET)

In modern Western music, the octave is divided into 12 equal logarithmic intervals. The frequency ratio between every adjacent semitone is the twelfth root of two (¹²√2 = 2^1/12 ≈ 1.059463).

f=440·2^{(k − 49) / 12}

Acoustic Standing Waves & Resonators

To produce C#3, open cylindrical organ pipes require an acoustic length of λ / 2 ≈ 123.8 cm, while closed resonators resonate at a quarter-wavelength λ / 4 ≈ 61.9 cm.

soundnote-to-frequency Lab Verified

Focusrite Scarlett 2i2 3rd Gen

Cea mai populara interfata audio USB

Air mode

Low latency

Doar 2 intrari

$179

4.8(15,432)

View on Amazon

Paid link • Amazon

Traian AnghelAuthor & Reviewer

Physics Teacher & Educational Technologist • Brăila, Romania

Last Reviewed: August 2026

Wave Lab calculators are constructed using rigorous peer-reviewed physics formulas from verified metrological repositories. Every equation, spectral conversion, and acoustic property is tested against NIST, CIE, and ISO datasets.

Verified Sources:NIST CODATACIE 1931 2° ObserverNASA Glenn Research