Frequency to Note Calculator
Any frequency in hertz maps to a position on the musical scale, and this calculator finds it. Using twelve-tone equal temperament, it measures how many semitones a frequency lies from a reference A4, rounds to the nearest note, and reports the note name, octave, and how many cents sharp or flat the pitch is. The A4 reference defaults to the 440 Hz concert standard but is editable, so you can convert against orchestral tunings of 442 or historical pitches like 415 Hz.
Frequency to note formula
n = 12 * log2( frequency / A4 ) (semitones from A4)
nearest semitone = round(n)
cents = (n - nearest semitone) * 100
note index = (nearest semitone + 9) mod 12 (A = 9 in the octave)
exact note frequency = A4 * 2 ^ (nearest semitone / 12)
The octave is derived by counting semitones above C0. Equal temperament spaces each semitone by a frequency ratio of the twelfth root of 2, about 1.059463.
Music tuning facts
- A4 at 440 Hz is the international concert pitch standardised by ISO 16.
- An octave doubles the frequency: A5 is 880 Hz when A4 is 440 Hz.
- There are 1,200 cents in an octave and 100 cents in a semitone.
- Equal temperament splits the octave into twelve equal semitones.
- Some orchestras tune to 442 or 443 Hz; baroque pitch is often around 415 Hz.
Frequency to note: frequently asked questions
How do you convert frequency to a musical note?
In twelve-tone equal temperament, the number of semitones from A4 is 12 times the base-2 logarithm of the frequency divided by the A4 reference (usually 440 Hz). Rounding gives the nearest note; the leftover fraction times 100 gives the deviation in cents. This calculator does that and names the note and octave.
What is A4 and why is it 440 Hz?
A4 is the A above middle C, the standard tuning reference. 440 Hz is the international concert pitch standardised by ISO 16. Some orchestras tune to 442 or 443, and historical performances may use 415. This calculator lets you set the A4 reference so you can convert relative to any tuning.
What are cents?
A cent is one hundredth of a semitone, so there are 1,200 cents in an octave. Cents measure how far a frequency is from the nearest note in equal temperament. A reading of 0 cents is perfectly in tune; plus or minus a few cents is usually imperceptible, while 20 or more is clearly audible.
What is equal temperament?
Twelve-tone equal temperament divides the octave into twelve equal semitones, each a frequency ratio of the twelfth root of 2 (about 1.0595). It is the standard tuning for pianos and most Western instruments because it lets you play in any key with consistent intervals, at the cost of slightly impure harmonies.
How are octaves numbered?
This calculator uses scientific pitch notation, where middle C is C4 and A4 is 440 Hz by default. Octave numbers increase at each C. So the B just below C4 is B3, and the note an octave above A4 is A5 at 880 Hz. The octave shown is derived from the semitone offset from A4.
Official sources
- International Organization for Standardization: ISO 16 standard concert pitch (A4 = 440 Hz).
- National Institute of Standards and Technology (NIST): The hertz and SI units.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.