About the Note Frequency Calculator
This note frequency calculator works both ways. Type a note name with its octave (C4, F#2, Bb5) to get its exact frequency in hertz, or enter a frequency to find the nearest equal-tempered note and how many cents sharp or flat it is. You also get the MIDI note number, the period of one cycle and the wavelength of the sound in air.
It is useful for tuning instruments, setting synth oscillators and filters, checking a tuner reading, picking EQ frequencies for a mix, building audio test signals and studying acoustics. You can change the reference pitch from the standard A4 = 440 Hz to alternatives such as 442 Hz (common in orchestras) or 432 Hz, and every result updates.
Frequencies use twelve-tone equal temperament, the tuning used by pianos, guitars and nearly all modern instruments, with scientific pitch notation where middle C is C4 and MIDI note 60. Wavelength assumes sound travels at 343 m/s, which is the speed in dry air at about 20 °C.
How to use the note frequency calculator
- 1Choose whether you are converting a note to a frequency or a frequency to a note.
- 2Type the note with its octave number (for example C4 or F#2), or enter the frequency in Hz.
- 3Leave the reference at 440 Hz unless your band, orchestra or recording uses another A4.
- 4Read the frequency, nearest note and cents offset; positive cents mean sharp, negative mean flat.
- 5Use the octave table to see the same note across the whole keyboard.
Formula and method
In twelve-tone equal temperament each semitone multiplies frequency by the twelfth root of two (about 1.05946), so an octave (12 semitones) exactly doubles it. Notes are numbered with MIDI numbers, where A4 is 69 and middle C (C4) is 60; the frequency of note n is the reference A4 multiplied by 2 raised to (n − 69)/12.
Going the other way, the exact (fractional) note number of a frequency is 69 + 12·log₂(f/A4). Rounding gives the nearest note, and the leftover fraction × 100 is the offset in cents (100 cents = one semitone). Period is 1/f, and wavelength is the speed of sound (343 m/s in air at 20 °C) divided by f.
- f
- Frequency in hertz (cycles per second)
- A4
- Reference pitch of A above middle C, normally 440 Hz
- n
- MIDI note number (C4 = 60, A4 = 69)
- cents
- Hundredths of a semitone; ±50 cents is the halfway point to the next note
Worked examples
Middle C at standard pitch
C4 is MIDI note 60, nine semitones below A4. Its frequency is 440 × 2^(−9/12) = 261.626 Hz, so one cycle lasts 3.822 ms and the sound wave in air is about 1.31 m long.
A 450 Hz tone — which note is it?
12 × log₂(450/440) = 0.389 semitones above A4, so the nearest note is A4 and the tone is about 38.9 cents sharp — clearly audible as out of tune, but not yet closer to A♯4.
Low E string tuned to A = 432 Hz
E2, the guitar’s low E string, is 29 semitones below A4. With A4 at 432 Hz its frequency is 432 × 2^(−29/12) = 80.91 Hz, compared with 82.41 Hz at standard 440 Hz pitch.
Frequently asked questions
What is the frequency of middle C?+
Middle C (C4) is 261.63 Hz in standard tuning with A4 = 440 Hz. With A4 = 442 Hz it rises to about 262.81 Hz, and with A4 = 432 Hz it falls to about 256.87 Hz.
Why is A4 440 Hz?+
A4 = 440 Hz was adopted as international standard concert pitch (ISO 16) so instruments made and tuned in different places agree. Some orchestras tune slightly higher, around 442–443 Hz, for a brighter sound.
What is a cent in music?+
A cent is one hundredth of an equal-tempered semitone, so an octave contains 1,200 cents. A note 50 cents sharp is exactly halfway to the next semitone; trained ears notice differences of roughly 5 cents.
How do I calculate the frequency of a note one octave higher?+
Double it. Each octave up multiplies the frequency by 2 and each octave down halves it, so A3 is 220 Hz, A4 is 440 Hz and A5 is 880 Hz in standard tuning.
Which octave number is middle C?+
In scientific pitch notation middle C is C4 and MIDI note 60. Some DAWs and synths label it C3 instead, so check your software if note names seem one octave off.
What frequency range can humans hear?+
Healthy young ears hear roughly 20 Hz to 20,000 Hz. The 88-key piano spans A0 (27.5 Hz) to C8 (4,186 Hz); harmonics above that give instruments their tone colour.