Note Frequency Calculator - Hz, MIDI Number, and Semitone Offset

The note frequency calculator turns any note name and octave into a frequency in hertz using the equal-tempered scale, with the international standard 440 Hz reference built in. Type a note such as A4, C#5, or Db3, choose your reference pitch, and the result panel reports the Hz value, the semitone offset from the reference, and the MIDI number so the answer can be cross-checked against any published frequency chart. The page covers everyday cases (find the Hz of middle C, verify the Hz of A4, check an octave doubling) and practical cases (tune a synth to 442 Hz, transpose for baroque rehearsal, name a sample-pack note by MIDI number).

• • Producers and engineers: Find the exact Hz of a synth patch or sample by typing the note name so a tuning change can be made in cents or Hz.
• • Band and orchestra players: Switch the reference to 442 Hz or 415 Hz to rehearse at a concert or baroque pitch.
• • Music students: Check a homework answer by reading the semitone offset and MIDI number next to the Hz, which makes the equal-tempered math auditable.

The result panel keeps the Hz value, the semitone offset, and the MIDI number on one screen, so a user with a target Hz can check the MIDI number for a named sample or patch.

Switching the enharmonic spelling does not change the Hz result because the pitch class is the same; it only changes the rendered note name, which helps when a key signature calls for flats instead of sharps.

When the question is which notes belong to a key rather than which Hz belongs to a note, music scale calculator lists the spelled scale from the same root and the same enharmonic preference.

The note frequency calculator parses the note name into a pitch class and an octave, converts the pitch class to a chromatic index 0-11, builds a MIDI note number, counts the semitones from the reference note, and multiplies the reference frequency by 2 to the power of (semitones / 12).

• noteName: A pitch class (C, C#, D, Eb, E, F, F#, G, G#, A, Bb, B) followed by an octave number 0-8, default A4.
• referenceHz: The frequency in Hz assigned to the reference note, default 440 Hz, with 20-2000 Hz allowed.
• referenceNoteName: The note that owns referenceHz, default A4 so the table matches ISO 16:1975.
• enharmonic: Sharp or flat spelling for the pitch class; the Hz result is identical because the chromatic index is the same.

An octave is always exactly a factor of two, because twelve semitones with the 2^(semitones/12) ratio produce 2^1 = 2. Doubling or halving the Hz value without touching the reference is therefore the fastest way to sanity-check a note-frequency result.

According to Britannica (tuning and temperament), equal temperament divides the octave into twelve identical semitone steps

If the next step is to move a melody up or down by a number of semitones, music transposer applies the same 2^(semitones/12) ratio to every note in the input.

Four ideas describe every note-frequency result the calculator produces.

Equal temperament and the 440 Hz reference let one formula cover every note on the keyboard; only the reference Hz has to change for a different tuning (baroque at 415 Hz, concert at 442 Hz).

The semitone offset is the most useful debugging tool because it is the exponent in the formula; if the offset looks wrong (say, 13 instead of 12 for an octave), the note name was probably mis-parsed and the Hz value will be off by a factor of 2.

When the user already has a wavelength or a period and needs the Hz value, frequency calculator applies the same Hz-based math on any input without a note name.

Five steps cover a single note lookup and a tuning change for a different reference pitch.

1. 1 Type the note name: Enter a letter A through G, an optional sharp (#) or flat (b), and an octave number 0-8. Default is A4, the ISO 16:1975 reference.
2. 2 Set the reference pitch: Leave the reference at 440 Hz for ISO standard tuning, type 442 Hz for concert pitch, or 415 Hz for baroque rehearsal.
3. 3 Pick the enharmonic spelling: Use sharp for key signatures with sharps and flat for keys with flats. The Hz result is identical either way.
4. 4 Read the Hz, semitone offset, and MIDI number: The result panel shows the frequency, the signed semitone count from the reference, and the MIDI note number.
5. 5 Use the result: Copy the Hz value into a synth or DAW, use the MIDI number to address a sampler, and use the semitone offset to confirm a transposition is the right number of steps.

Type C4, leave the reference at 440 Hz, and the result is 261.6256 Hz with -9 semitones from A4 and MIDI 60. Change the reference to 415 Hz and the same C4 reads 246.9417 Hz with -9 semitones, which is the baroque version of middle C.

When the user wants to verify the math by hand, log 2 calculator applies the same binary-logarithm step that turns the semitone offset into the frequency ratio.

A purpose-built tool keeps the equal-tempered math, the reference pitch, and the enharmonic spelling in one place.

• • Hz, semitone offset, and MIDI number on one screen: The result panel shows the three numbers a musician or producer needs to cross-check a frequency against any published chart or sample library.
• • Configurable reference pitch: Switch between 440 Hz ISO standard, 442 Hz concert, and 415 Hz baroque without retyping the note name, so a rehearsal or set list can be retuned in one place.
• • Sharp or flat spelling without a different result: Pick the spelling that fits the key signature and trust the Hz value to stay the same, because the chromatic index is identical for C# and Db.
• • Auditable calculation: The worked examples and the formula box show how the Hz value is built from the semitone offset, so a teacher or student can defend the answer on an exam.
• • Works for every note on the standard keyboard: The parser accepts all twelve pitch classes and octaves 0 through 8, so the same form covers a sub-bass note and a high register note without retuning.

The combination of the Hz value and the MIDI number means the page is useful for both acoustic reference (tune an instrument) and digital reference (address a sampler or a virtual instrument).

For a transposition that keeps every chord quality and slash-bass note intact while reusing the same semitone math, chord transposer shifts an entire chord progression to a new key with the same enharmonic preference used on this page.

Three variables drive the Hz value, and two limitations tell you when to reach for a different tool.

• • The calculator returns the equal-tempered value, which is the standard for modern pianos, synths, and digital audio. Just-intonation or other historical tunings are not modeled and would return slightly different cents on most intervals.
• • The page covers octaves 0 through 8 because that range covers the standard 88-key piano. MIDI note numbers outside 12 to 108 are still computable, but the Hz values fall outside the audible range and the result is reported for completeness only.

If the result looks wrong, the fastest sanity check is the semitone offset: it should match the difference between the chosen MIDI number and 69, and it should be zero when the note is A4 with the default reference.

Switching the reference from 440 Hz to 415 Hz applies the same 0.943 ratio to every Hz value, so the result of the page can be retuned by a single constant without retyping the note name.

According to ISO 16:1975, the standard tuning pitch for the note A above middle C is 440 Hz

If the user is reasoning about a sound wave rather than a pitch, wave speed calculator turns a frequency, a wavelength, or a period into the other two units using the same Hz-based math.