Note Frequency Calculator - MIDI, Hz & Note Name Converter

Equal temperament formula

f = A4 × 2^((n − 69) / 12)

Where n is the MIDI note number. A4 = MIDI 69. Middle C (C4) = MIDI 60. Each octave doubles frequency; each semitone multiplies by 2^(1/12) ≈ 1.0595.

MIDI note range

MIDI note numbers run from 0 (C−1, ~8 Hz) to 127 (G9, ~12,544 Hz).

Note frequency reference table

Concert pitch and tuning systems

A4 = 440 Hz became the international standard in 1939 (ISO 16). However, orchestras routinely deviate: many European orchestras tune to A4 = 442 Hz or 443 Hz for a brighter sound. Baroque ensembles performing historical repertoire often use A4 = 415 Hz (exactly one semitone below modern pitch). A difference of 4 Hz between 440 and 444 Hz is clearly audible as a slight "brightness" difference when the two play simultaneously, heard as about 4 beats per second at A4.

Why equal temperament?

Equal temperament divides the octave into 12 equal semitones, each with a frequency ratio of 2^(1/12) ≈ 1.0595. This means every key sounds equally in-tune (and equally slightly out-of-tune). In contrast, just intonation uses pure integer ratios (a perfect fifth is exactly 3:2), which sounds pure and resonant in the key it is tuned to but produces noticeably out-of-tune intervals in distant keys. Equal temperament is the practical compromise that allows a single instrument to play in any key without retuning.

Frequency and pitch perception

Human pitch perception is logarithmic: an octave is always a 2× frequency increase, regardless of register. This is why the distance from A2 (110 Hz) to A3 (220 Hz) sounds the same as A3 to A4 (440 Hz), even though the second interval spans twice as many Hz.

Cents provide a finer unit: 100 cents = 1 semitone, 1200 cents = 1 octave. Pitch differences below about 5 cents are imperceptible to most trained listeners. Professional tuning targets are typically within ±2 cents of the reference pitch.