Frequency to Musical Note Converter (Hz)
Convert a frequency in Hz to the nearest musical note and octave with cents detuning, using equal temperament and an adjustable A4 reference. Runs in your browser.
Concert pitch is 440 Hz; some orchestras use 442/443.
In 12-tone equal temperament, the note number is 12·log₂(frequency ÷ A4) + 69 (the MIDI scale, where A4 = 69). The nearest whole number gives the note name and octave; the fractional part, ×100, is how many cents the pitch is sharp (+) or flat (−) of that note. A semitone is 100 cents; ±50¢ is the boundary to the next note. Everything runs in your browser.
About this tool
Every musical pitch corresponds to a sound-wave frequency measured in hertz (Hz), and this converter maps any frequency to the nearest note in the standard 12-tone equal temperament system. The reference point is concert pitch: the A above middle C (A4) is defined as 440 Hz, and from there every other note is spaced by equal ratios — each semitone multiplies the frequency by the twelfth root of two (about 1.0595), so twelve semitones double the frequency to the octave. The tool inverts that relationship using the formula note number = 12 · log₂(frequency ÷ A4) + 69, which yields the MIDI note number; rounding to the nearest whole number gives the note name and octave, and the leftover fraction, multiplied by 100, tells you how many cents the pitch sits sharp or flat of that exact note (a cent is one-hundredth of a semitone, and ±50 cents is the midpoint to the neighboring note). That cents reading makes the tool useful as a reference tuner: feed it a measured frequency and see not just which note it is but how far out of tune. The A4 reference is adjustable because not everyone tunes to 440 — many European orchestras tune slightly higher to 442 or 443 Hz for a brighter sound, Baroque ensembles often use 415 Hz (about a semitone lower), and changing it shifts the whole mapping accordingly. It also reports the MIDI note number, handy for music software and hardware. Note that this uses equal temperament, where every semitone is identical; 'just intonation' and other historical tunings place some notes at slightly different frequencies, so a perfectly tuned just-intonation interval may read a few cents off here. Everything runs in your browser; nothing is uploaded.
How to use it
- Enter the frequency in hertz (Hz).
- Adjust the A4 reference if you tune to something other than 440 Hz (e.g. 442 or 415).
- Read the nearest note name, octave, and how many cents sharp or flat it is.
- Use the exact note frequency and MIDI number for tuning or music software.
Frequently asked questions
- How do you convert frequency to a musical note?
- Use note number = 12 · log₂(frequency ÷ 440) + 69. Rounding gives the MIDI note (and thus the note name and octave); the fractional part × 100 is the cents the pitch is sharp or flat of that note.
- What note is 440 Hz?
- A4 — the A above middle C — is 440 Hz by international standard (concert pitch). It is the reference from which all other equal-temperament frequencies are derived.
- What are cents?
- Cents measure pitch deviation: one semitone is 100 cents. A reading of +10 cents means the frequency is 10 cents sharp (slightly higher) than the nearest note; ±50 cents is exactly halfway to the adjacent note.
- Why can I change the A4 reference?
- Not all music tunes to 440 Hz. Many orchestras use 442–443 Hz for a brighter tone, and Baroque performance often uses 415 Hz (roughly a semitone lower). Changing the reference shifts the entire frequency-to-note mapping.
- What is equal temperament?
- A tuning system that divides the octave into 12 equal semitones, each a frequency ratio of 2^(1/12). It is the standard for pianos and most modern music. Other systems (just intonation) use slightly different ratios for purer-sounding intervals.
- Why does a perfectly tuned interval read a few cents off?
- This tool uses equal temperament. In just intonation, intervals like the major third are tuned to simple whole-number ratios that differ from equal temperament by several cents, so they will not read exactly 0 here.