Frequency to Note
Enter a frequency in hertz to find the nearest musical note and how many cents sharp or flat it is.
445 Hz is closest to A4, whose exact pitch is 440 Hz. That is +19.6 cents sharp, so tune down slightly.
To turn a frequency into a note, count semitones from A4 with n = 12 × log₂(f ÷ 440) and round to the nearest note. So 440 Hz is A4, 0 cents — perfectly in tune — while 445 Hz rounds to the same A4 but sits about +20 cents sharp.
How a frequency becomes a note
Every pitch is a frequency in hertz (Hz) — how many times per second the wave repeats. In 12-tone equal temperament the octave is split into twelve equal semitones, so each semitone multiplies the frequency by the twelfth root of two (≈ 1.059463). Measuring how many semitones a frequency lies above or below A4 = 440 Hz, then rounding to the closest whole semitone, gives the nearest note. The leftover fraction, expressed in cents, tells you how sharp or flat the pitch is — exactly what a guitar tuner shows.
n is the number of semitones from A4; round it to the nearest note, and cents = 100 × (n − round(n))
Worked example
Identify the note for a measured pitch of 261.63 Hz.
- 1 Count semitones from A4. n = 12 × log₂(261.63 ÷ 440) = 12 × log₂(0.594614) ≈ −9.00 semitones.
- 2 Round to the nearest note. round(−9.00) = −9, so the note is nine semitones below A4.
- 3 Name that note. MIDI 69 + (−9) = 60, which is C4 — middle C.
- 4 Read the cents deviation. 100 × (−9.00 − (−9)) ≈ 0 cents, so 261.63 Hz is C4, perfectly in tune.
Reference frequencies (A4 = 440 Hz)
Equal-tempered frequencies rounded to two decimals. A pitch landing between two rows is named by whichever is nearest, with the gap reported in cents.
| Note | Frequency (Hz) |
|---|---|
| C4 (middle C) | 261.63 |
| E4 | 329.63 |
| G4 | 392.00 |
| A4 (concert pitch) | 440.00 |
| C5 | 523.25 |
| E2 (guitar low E) | 82.41 |
| E4 (guitar high E) | 329.63 |
Reading the result
What cents mean. A cent is one hundredth of a semitone, so an octave holds 1200 cents and a single semitone holds 100. This tool reports a value from −50 to +50: a positive number means the pitch is sharp (higher than the target note) and negative means flat (lower). Most listeners only notice errors beyond roughly 5–10 cents.
Changing the reference. A4 = 440 Hz is the modern standard, but you can set a different reference — 442 or 443 Hz for a brighter orchestral sound, or 432 Hz. Raising the reference shifts every note name boundary up in frequency, so the same measured Hz can round to a different cents offset.
Why your note reads sharp or flat. Strings drift as they stretch and as temperature changes, and a hard pluck or a bent note briefly raises the pitch. If the cents value is small, a tiny turn of the tuning peg toward the target frequency brings it to zero.