Note Frequency Calculator
Find the exact frequency in hertz of any musical note from A440 tuning — pick a note and octave and get its pitch, MIDI number and period.
How it works
f = A4 × 2^((MIDI − 69) ÷ 12), where MIDI = 12 × (octave + 1) + note index and A4 (concert pitch) is 440 Hz by default
Equal temperament divides every octave into 12 equal semitones, so each step multiplies frequency by the twelfth root of two (about 1.0595). Pitch is measured from the reference A above middle C — A4, conventionally 440 Hz (MIDI note 69). Any note is that reference scaled by two raised to the power of its semitone distance divided by twelve. Doubling the frequency raises the pitch exactly one octave, which is why A5 is 880 Hz and A3 is 220 Hz.
Worked example
A4 is the reference at 440 Hz (MIDI 69). Middle C (C4) sits nine semitones below A4, so its frequency is 440 × 2^(−9/12) ≈ 261.63 Hz. Raise the tuning reference to A4 = 442 Hz and every note scales up by the same 0.45%.
Frequently asked questions
Why is A4 = 440 Hz the standard?
A440 was adopted as the international concert-pitch standard (ISO 16) in the mid-20th century. Some orchestras tune slightly higher (A442 or A443) for a brighter sound, and historically informed ensembles often use A415 for baroque music — change the reference field to match.
What is the MIDI number for?
MIDI note numbers run 0–127 with middle C at 60 and A4 at 69. They are how keyboards and software identify pitches, so this figure lets you match a note directly to a synth, sampler or DAW.
How is frequency related to the period?
The period is the time for one complete vibration and equals 1 ÷ frequency. At 440 Hz the string or air column completes 440 cycles per second, so one cycle takes about 2.27 milliseconds.
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This calculator is for educational purposes. Double-check important results before acting on them.