Note Frequency Calculator - MIDI, Hz & Note Name Converter

How to use this tool

1. Enter a note name (e.g. C4, A#3, Bb5), a MIDI number (0–127), or a frequency in Hz.
2. All three representations are shown instantly.

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.

The calculator’s tuning selector supports A4 = 440 Hz (standard), 432 Hz, 415 Hz (Baroque), 442 Hz (orchestra), and 444 Hz. These are reference pitches for the equal-tempered note calculations; changing the selector recalculates the interactive result and its wave readouts.

Approximate sound wavelength and period

For each result, wavelength is estimated as 343 m/s divided by the displayed frequency, and period is 1,000 milliseconds divided by that frequency. The 343 m/s speed of sound is an approximation for dry air at 20°C, so actual wavelength changes with air temperature and conditions. For example, standard A4 at 440 Hz has a wavelength of about 0.780 m and a period of about 2.273 ms. These calculations use the displayed equal-tempered note frequency; in Frequency (Hz) mode, they describe the nearest note shown by the calculator rather than the exact entered frequency. See the NASA Technical Reports Server reference on sound in dry air at 20°C for the approximate sound speed.

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.