Note Frequency Calculator - Note to Hz & MIDI Number

Every note you play has a fundamental frequency — the number of times per second the sound wave repeats. In the twelve-tone equal temperament system used by virtually all modern instruments, DAWs, and synthesizers, that mapping is fixed by a single anchor: the A above middle C, called A4, is tuned to a reference frequency (440 Hz by international standard), and every other note is derived from it. Each semitone step multiplies or divides the frequency by the twelfth root of two, roughly 1.0595, so twelve steps — one octave — exactly doubles or halves it. That is why A3 is 220 Hz, A4 is 440 Hz, and A5 is 880 Hz. The calculator uses the MIDI numbering scheme that sequencers and synths share. Middle C (C4) is MIDI note 60, A4 is MIDI note 69, and each octave spans twelve numbers, so a note's number is 12 times its octave plus one, plus its position within the octave counting from C. Once the MIDI number is known, the frequency is the reference pitch multiplied by 2 raised to the power of the distance from 69, divided by 12. With the standard 440 Hz reference, middle C works out to 261.63 Hz and the lowest piano note, A0, to 27.50 Hz. The A4 reference field matters more than many players expect. Orchestras in parts of Europe tune to 442 or 443 Hz for a slightly brighter ensemble sound; period ensembles playing Baroque repertoire often use 415 Hz, almost exactly a semitone below modern pitch; and a popular internet tuning, 432 Hz, sits about 32 cents flat of standard. Change the reference and every note in the table shifts proportionally, which is exactly how the calculator handles it — the ratios between notes never change, only the anchor does. The wavelength column divides the speed of sound in air at room temperature, 343 meters per second, by the frequency. It is practical, not academic: a 55 Hz bass note is over six meters long, which explains why small rooms struggle with low-end buildup and why bass traps target corners, while a 4,186 Hz piano top C is barely eight centimeters and beams directionally. Speaker builders, acousticians, and studio designers use these lengths to place absorbers, size ports, and predict room modes. Producers also lean on note-to-frequency conversion when mixing: tuning a kick drum's fundamental to the track's key, setting a synth oscillator in hertz, notching a resonance that sits exactly on an offending note, or dialing a sub-bass to E1 at 41.20 Hz instead of guessing. The octave table gives you the full context at a glance so you can find neighboring notes without recalculating.