Free Online Musical Note Frequency Calculator
Find the frequency of any note and octave.
Concert pitch is normally 440 Hz. Orchestras sometimes tune to 442 or 443 Hz.
Equal temperament divides the octave into twelve equal semitone ratios. The frequency ratio between adjacent semitones is the twelfth root of two, approximately 1.059463.
Chromatic scale in the selected octave
| Note | Frequency | Cents from A440 | MIDI |
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About the Musical Note Frequency Calculator
Every musical note corresponds to a specific frequency of vibration. The modern Western tuning system uses equal temperament, which divides the octave into twelve semitones with a constant frequency ratio between neighbours. This calculator converts a note name and octave into hertz, shows the MIDI note number, reports the deviation in cents from standard A440 equal temperament, and lists the complete chromatic scale for the selected octave. It is useful for tuning instruments, programming synthesisers, setting filter cutoffs, and understanding how note names map onto frequencies.
The equal temperament formula
Frequencies are anchored at A4, which is normally 440 Hz. The formula is f = A4 × 2(n / 12), where n is the number of semitones away from A4. Moving up twelve semitones doubles the frequency; moving down twelve semitones halves it. MIDI note 69 is A4, middle C is MIDI 60 (C4), and each semitone changes the MIDI number by one. The frequency ratio for a single semitone is the twelfth root of two, about 1.059463. This constant ratio is what makes equal temperament possible, although it means that most intervals are slightly out of tune compared with pure ratios.
Cents and tuning references
A cent is one hundredth of an equal-tempered semitone. The formula for the interval in cents between two frequencies is 1200 × log₂(f₁ / f₂). If an orchestra tunes A4 to 442 Hz instead of 440 Hz, every note shifts upward by about 7.85 cents. The calculator reports the cents deviation from A440 so you can see the effect of changing the reference pitch. Instrument tuners often display cents as a needle scale, where zero is perfectly in tune and ±50 cents reaches the neighbouring semitone.
Octave numbering
Scientific pitch notation places middle C at C4. The octave number increases at each C, so B3 is the note just below middle C and C4 begins the next octave. MIDI numbering follows a different convention: middle C is 60 in the common standard, although some software labels it 72 or uses C3 instead of C4. This page uses the widely adopted convention where C4 = MIDI 60 and A4 = MIDI 69. Octave 0 begins near 16 Hz for C0, while octave 9 extends beyond the range of human hearing.
Practical uses
- Tune a guitar, violin, or wind instrument against a reference tone.
- Set oscillator frequencies in a synthesiser or modular patch.
- Calculate filter cutoffs and formant frequencies in audio processing.
- Design chimes, bells, or tuned percussion with specific fundamental pitches.
- Compare historical pitch standards such as A415, A430, or A466.
Frequently asked questions
Why is A4 set to 440 Hz?
440 Hz became the international concert pitch standard in the twentieth century. It is a convention rather than a law of physics, and some ensembles prefer 442 or 443 Hz for a brighter sound.
Does a higher reference pitch change the note names?
No. The note names and MIDI numbers stay the same; every frequency shifts proportionally. The cents display shows how far the chosen reference is from A440.
Why does the wavelength matter?
Wavelength helps with room acoustics, instrument design, and microphone placement. It is the speed of sound divided by frequency, so low notes have long wavelengths and high notes have short ones.