Note Frequency Converter — notes to hertz, hertz to notes

This note frequency converter turns a musical note name into a frequency in hertz, and turns any measured frequency back into the nearest note plus the exact cents deviation from it. It works across the full audible range, from the lowest organ pedal notes to the top of a piccolo's register, and it lets you set the reference pitch yourself instead of assuming everyone in the room has agreed on 440 Hz. Type a value, choose the direction, and the answer updates as you type.

Arb Digital publishes a large library of free technical converters, and this one fills a gap that generic unit tools leave open. A unit converter can tell you that 2.5 kHz is 2,500 Hz. It cannot tell you that 2,500 Hz is 14 cents sharp of D#7. That second question is the one musicians, audio engineers and instrument builders actually ask, and answering it needs the equal-temperament model built in.

What This Note Frequency Converter Does

Musical pitch and frequency are two descriptions of the same physical thing. A vibrating string, column of air or loudspeaker cone repeats its motion a certain number of times per second, and that repetition rate is the frequency, measured in hertz. The human ear does not hear those hertz on a linear scale, though. It hears ratios. Doubling a frequency always sounds like the same distance upward — one octave — whether you go from 55 Hz to 110 Hz or from 1,760 Hz to 3,520 Hz.

Twelve-tone equal temperament takes that octave and divides it into twelve equal steps, where equal means equal in ratio rather than equal in hertz. Each semitone is a frequency ratio of the twelfth root of two, roughly 1.059463. Stack twelve of them and you land on exactly double, which is what makes the system close on itself and lets an instrument play in every key without retuning.

The converter runs that model in both directions. Give it a note name and it returns the exact frequency for your chosen reference pitch. Give it a frequency and it finds the closest note, then reports how far off you are in cents. The four supporting readouts show the nearest note name, the cents deviation, the MIDI note number and the period of one cycle in milliseconds, so a single input answers the musical question, the digital-instrument question and the timing question at once.

How to Use It

1. Enter your value. A note name like A4, C#3, Bb5 or F-1, or a plain frequency in hertz such as 261.63.
2. Set the From and To fields. Note name to frequency for writing a synth patch or checking a tone generator; frequency to note name for identifying something you measured.
3. Adjust the reference pitch if you need to. The A4 box defaults to 440 Hz, but 432 Hz and 442 Hz are both in real use and are set here rather than worked around.
4. Choose sharps or flats for how the answer is spelled. This changes the label only, never the pitch.
5. Read the cents figure in the grid. That is the tuning number — positive means sharp of the nearest note, negative means flat.

The Formula: How Note Frequency Is Calculated

Every note is addressed by a MIDI note number, an integer that counts semitones upward with middle C sitting at 60 and the A above it at 69. Converting a MIDI number to a frequency is a single exponential:

f = reference × 2^{(m − 69) ÷ 12}

Here m is the MIDI note number and reference is your A4 pitch in hertz. Because A4 is MIDI 69, the exponent is zero for A4 and the formula returns the reference pitch unchanged, which is the property that makes the reference field meaningful rather than decorative. The inverse is a base-two logarithm:

m = 69 + 12 × log₂(f ÷ reference)

That inverse usually produces a number with a fractional part. Rounding it to the nearest integer gives the nearest note; the leftover fraction, multiplied by one hundred, is the cents deviation. A cent is one hundredth of a semitone, so there are 1,200 cents in an octave, and the whole system is logarithmic by construction. If you want to see the underlying log arithmetic on its own, our logarithm calculator handles base conversions directly. The hertz itself is the SI unit of frequency, defined in the BIPM SI Brochure as one cycle per second, and the note-to-MIDI-to-frequency relationships used here match the tables published by the UNSW School of Physics music acoustics group.

Reference Table: Note Frequencies at A4 = 440 Hz

Frequencies below are in hertz for the twelve chromatic notes across the central octaves, rounded to two decimals. Every octave up doubles the number and every octave down halves it, so you can extend this table in either direction with mental arithmetic alone.

• C — C2 65.41, C3 130.81, C4 261.63, C5 523.25, C6 1046.50
• C# / Db — C#2 69.30, C#3 138.59, C#4 277.18, C#5 554.37, C#6 1108.73
• D — D2 73.42, D3 146.83, D4 293.66, D5 587.33, D6 1174.66
• D# / Eb — D#2 77.78, D#3 155.56, D#4 311.13, D#5 622.25, D#6 1244.51
• E — E2 82.41, E3 164.81, E4 329.63, E5 659.26, E6 1318.51
• F — F2 87.31, F3 174.61, F4 349.23, F5 698.46, F6 1396.91
• F# / Gb — F#2 92.50, F#3 185.00, F#4 369.99, F#5 739.99, F#6 1479.98
• G — G2 98.00, G3 196.00, G4 392.00, G5 783.99, G6 1567.98
• G# / Ab — G#2 103.83, G#3 207.65, G#4 415.30, G#5 830.61, G#6 1661.22
• A — A2 110.00, A3 220.00, A4 440.00, A5 880.00, A6 1760.00
• A# / Bb — A#2 116.54, A#3 233.08, A#4 466.16, A#5 932.33, A#6 1864.66
• B — B2 123.47, B3 246.94, B4 493.88, B5 987.77, B6 1975.53

Only the A row contains whole numbers, and that is not a coincidence — every other value is an irrational multiple of the reference, so the two-decimal figures above are rounded rather than exact.

Why the Reference Pitch Is an Input, Not a Constant

Most note tables hard-code 440 Hz and stop there. In practice the reference moves. Many European orchestras tune sharper, commonly to 442 Hz or 443 Hz, because a slightly higher pitch is perceived as brighter and more projecting. Some ensembles and recording projects deliberately use 432 Hz. Historically informed performance of baroque repertoire often works around 415 Hz, which is close to a semitone below modern pitch and lets a performer read the written notes while the instrument sounds where the period expects.

The size of the shift matters more than it first appears. Moving from 440 Hz to 442 Hz is a change of about 7.85 cents across every note on the instrument — small enough to ignore when you are alone, large enough to sound unmistakably wrong against a fixed-pitch instrument tuned the other way. Moving from 440 Hz to 432 Hz is about 31.8 cents, roughly a third of a semitone, which no ensemble can absorb. Setting the reference in the box above rescales the whole chromatic scale at once, which is the only correct way to handle it: you do not shift one note, you shift the grid.

Reading the Cents Number Correctly

Cents exist because raw hertz differences are useless for comparing tuning across the range. Being 3 Hz flat at A2, where the note sits at 110 Hz, is a wildly noticeable error of about 47 cents. Being 3 Hz flat at A6, where the note sits at 1,760 Hz, is under 3 cents and essentially inaudible. The same hertz error means completely different things depending on where you are, and that is exactly the trap the cents readout removes.

The scale runs from −50 to +50 cents, because once you pass a half-semitone in either direction the nearest note becomes the next one along and the deviation flips sign. A reading of +49 cents is not a badly tuned note so much as an ambiguous one — you are almost exactly between two notes, and the tool has to pick a side. If you see a value near the edge of that range, check that your instrument is in the octave you think it is before chasing the tuning.

One practical consequence: a very small cents error on a single note is often not a tuning problem at all but a measurement problem. Analysis windows that are too short, vibrato, and the pitch instability of the first few milliseconds of a plucked or struck note will all move the reading by several cents. Let the tone settle before you trust the number.

Where Equal Temperament Stops Being Exactly Right

Twelve-tone equal temperament is a compromise, and knowing where it compromises explains a lot of otherwise confusing tuning behaviour. A pure perfect fifth is a frequency ratio of exactly 3:2. The equal-tempered fifth is slightly narrower, off by about two cents, which is small enough to pass unnoticed. The equal-tempered major third is the bigger casualty: a pure major third is a 5:4 ratio, and the tempered version sits roughly 14 cents sharp of it. That is why a sustained major chord on a piano sounds slightly restless compared with the same chord sung by a choir, which naturally drifts toward pure ratios.

This also explains why a good piano technician does not tune a piano to the exact numbers this converter produces. Real strings are stiff, and stiffness makes their overtones sit slightly higher than perfect whole-number multiples of the fundamental — a phenomenon called inharmonicity. To make octaves sound right to the ear, the technician stretches them, tuning the top of the instrument progressively sharp and the bottom progressively flat relative to theory. The calculated frequencies remain the correct starting reference; they are simply not the finishing point on a piano.

Frequency, Period and Wavelength From the Same Pitch

The period readout in the grid is the duration of a single cycle, equal to 1,000 divided by the frequency in hertz, expressed in milliseconds. It is the number you need when you are setting a delay time to match a pitch, sizing a buffer, or reasoning about the latency of a synthesis chain. A4 at 440 Hz has a period of about 2.27 ms; drop three octaves to A1 at 55 Hz and the period stretches to 18.18 ms.

Wavelength follows from the same frequency once you know the speed of sound, which is roughly 343 metres per second in air at 20 °C and changes with temperature. That relationship is why a room can reinforce some notes and swallow others: standing waves form where a room dimension lines up with a half wavelength. A 40 Hz bass note has a wavelength around 8.6 metres, longer than most domestic rooms, which is the physical reason low-frequency response is so hard to control indoors. If you need to move between metres per second and other speed units for that calculation, use our speed converter, and for the temperature side see the temperature converter.

How This Differs From a Plain Frequency Converter

Our frequency converter does unit conversion on the hertz scale — hertz to kilohertz, megahertz, gigahertz, RPM and radians per second — and it treats a frequency as a pure number with no musical meaning attached. This page does the opposite job: it maps between frequencies and the twelve-tone equal-tempered note grid, and every answer depends on a reference pitch that the plain converter has no concept of. Use the frequency converter when you are changing the unit; use this one when you are changing between a pitch name and a frequency.

Two other neighbours are worth naming so you land in the right place. Loudness is a different quantity entirely and belongs to the sound level converter, which handles decibels and sound pressure — a note's pitch and its volume share no arithmetic at all. And when a frequency comes back in exponent form from an analyser, the scientific notation converter will put it into plain decimal before you paste it in here.

Common Mistakes to Avoid

• Comparing tuning in hertz instead of cents — 3 Hz is a large error in the bass and an inaudible one in the treble.
• Forgetting to change the reference pitch when playing with an ensemble tuned to 442 Hz; every note shifts, not just the A.
• Assuming octave numbering starts where you expect — middle C is C4 in the scientific pitch notation used here, but some manufacturers label it C3 or C5.
• Treating calculated frequencies as final piano tuning targets, ignoring the stretch that inharmonicity requires.
• Measuring pitch from the attack of a note, where the reading is unstable, rather than from the sustained portion.

Related Free Tools From Arb Digital

Pair this with the frequency converter for hertz unit changes, the sound level converter for decibels, and the logarithm calculator if you want to work the cents formula by hand. The speed converter and temperature converter cover the speed-of-sound side of wavelength work, and the scientific notation converter tidies up exponent-form readings. The full free online tools hub lists every converter we publish.

Frequently Asked Questions