Note Frequency Calculator
With A4 at 440 Hz, middle C (C4) is 261.63 Hz and A4 is 440 Hz. Tune A4 to 432 Hz and C4 drops to 256.87 Hz. A 450 Hz tone is the nearest to A4, 38.9 cents sharp.
How to use
- Choose Note to frequency or Frequency to note.
- For a note, pick the note name and the octave from 0 to 8 (scientific pitch notation, where middle C is C4 and A4 is the tuning note). For a frequency, type the Hz value.
- Set the reference pitch for A4. 440 Hz is the standard, 432 Hz and 415 Hz (Baroque) are common alternatives, and any value from 300 to 600 Hz works.
- Optionally enter the air temperature in Celsius to adjust the speed of sound. Leave it empty to use 343 m/s.
- Read the frequency or the nearest note with its cents offset, the wavelength, and the table of all 12 notes in that octave. Press Play to hear a sine tone.
How it works
In 12-tone equal temperament every semitone is a factor of 2^(1/12). With MIDI note number n (C4 = 60, A4 = 69), the frequency is f = A4 x 2^((n - 69) / 12). Each octave doubles the frequency, so A3 is 220 Hz, A4 is 440 Hz and A5 is 880 Hz. The note number is n = (octave + 1) x 12 + semitones above C.
Frequency to note: n = 69 + 12 x log2(f / A4). The nearest whole n is the note, and the offset is cents = 100 x (n - nearest n), which equals 1200 x log2(f / f_note). A cent is 1/100 of a semitone, and most people notice errors beyond about 5 cents. A positive offset is sharp (high) and a negative one is flat (low).
Wavelength in air is the speed of sound divided by the frequency: wavelength = v / f. The tool uses 343 m/s, which is air at 20 °C. If you enter a temperature T in Celsius it uses v = 331.3 + 0.606 x T, a standard approximation for dry air. Humidity changes the speed slightly, and that is ignored.
The play button makes a pure sine wave with the browser Web Audio API, at a low volume, for 1.5 seconds. Pitches below 20 Hz or above 20,000 Hz are outside the range of hearing, and small speakers play very low notes quietly or not at all. Notes are equal-tempered, so a piano tuned with stretch tuning or a violin played in just intonation can differ by a few cents.
Octave 4 at A4 = 440 Hz
| Note | Frequency (Hz) | Wavelength (m) |
|---|---|---|
| C4 | 261.63 | 1.311 |
| D4 | 293.66 | 1.168 |
| E4 | 329.63 | 1.041 |
| F4 | 349.23 | 0.982 |
| G4 | 392.00 | 0.875 |
| A4 | 440.00 | 0.780 |
| B4 | 493.88 | 0.695 |
FAQ
What is the frequency of middle C?
Middle C is C4 and it is 261.63 Hz when A4 is 440 Hz. At A4 = 432 Hz it is 256.87 Hz, and at A4 = 415 Hz it is 246.76 Hz.
Why is A4 440 Hz?
It is the concert pitch standard, set by ISO 16 in 1955 after earlier conferences. Many orchestras tune a little higher, around 442 Hz, and Baroque ensembles often use 415 Hz, about a semitone lower.
What are cents?
A cent is one hundredth of an equal-tempered semitone, and 1200 cents make an octave. The cents value tells you how far a frequency is from the nearest note, between -50 and +50.
Is C4 or C3 middle C?
In scientific pitch notation middle C is C4, which is MIDI note 60. Some software calls the same key C3 or C5, so check which numbering your program uses.
Why does the wavelength change with temperature?
Sound travels faster in warmer air, about 0.6 m/s more per degree Celsius, so the same frequency has a longer wavelength. The effect is small, around 2 percent between 10 and 20 degrees.