Note Frequency Calculator
Calculate the frequency (Hz) of any musical note using standard A4=440 Hz tuning. Covers C0 to B8 across all 12 chromatic pitch classes.
How to use this tool
- Enter note and octave in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your frequency and the full breakdown beneath it.
Find the exact frequency (Hz) of any musical note. Uses A4=440 Hz equal temperament.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
MIDI note number = (octave + 1) × 12 + semitone index
Frequency (Hz) = 440 × 2(MIDI − 69) ÷ 12
Semitone indices (C=0, C#=1, D=2, D#=3, E=4, F=5, F#=6, G=7, G#=8, A=9, A#=10, B=11).
How it works
This calculator determines the exact frequency of any standard pitch by first mapping the note name and octave to its MIDI note number (middle C = 60, A4 = 69), then applying the equal-temperament formula referenced to A4 = 440 Hz. Each semitone upward multiplies frequency by 21/12 ≈ 1.05946. The result is exact under 12-tone equal temperament (12-TET); other tuning systems such as just intonation will differ.
Worked example
- Note = A, Octave = 4.
- MIDI = (4 + 1) × 12 + 9 = 60 + 9 = 69.
- Frequency = 440 × 2^((69 − 69) ÷ 12) = 440 × 2^0 = 440 × 1 = 440 Hz.
A4 = 440 Hz, MIDI note 69.
Common mistakes to avoid
- Selecting the wrong octave; middle C is C4 (261.63 Hz) in scientific pitch notation, but some DAWs display it as C3.
- Assuming A4 = 432 Hz tuning; this calculator uses standard A4 = 440 Hz, so results differ by about 32 cents if the instrument is tuned to 432 Hz.
- Confusing enharmonic equivalents; C# and Db are the same frequency in equal temperament, but picking the wrong spelling can cause confusion in notation.
Key terms
- Equal temperament (12-TET)
- A tuning system that divides the octave into 12 equal semitones, each with a frequency ratio of 2^(1/12) ≈ 1.05946.
- MIDI note number
- An integer from 0 to 127 that uniquely identifies a pitch in the MIDI standard. A4 = 69, middle C (C4) = 60.
- A4 = 440 Hz
- The international tuning reference pitch, standardised by ISO 16. All frequencies in this calculator are derived relative to this value.
- Octave
- A doubling of frequency. A5 is exactly twice the frequency of A4 (880 Hz vs 440 Hz).
- Semitone
- The smallest interval in 12-TET, equal to one step on the chromatic scale (e.g. C to C#).
Frequently asked questions
- What frequency is middle C?
- Middle C (C4) is approximately 261.63 Hz in standard A4=440 tuning.
- What is A4 in Hz?
- A4 is 440 Hz by international standard (ISO 16:1975).