Piano Note Frequency Calculator

A440 refers to the musical note A above middle C vibrating at exactly 440 Hz. It was adopted as the international standard concert pitch by ISO 16:1975 and has been widely used since the 1930s. Before standardisation, concert pitch varied widely by country and era, making it difficult for instrument makers and musicians to collaborate internationally. A440 provides a fixed reference point so that instruments manufactured and tuned independently will play in tune together. Some orchestras and early music ensembles use slightly different pitches (e.g., 442 Hz or 415 Hz), but A440 is the universal default.

Equal temperament is the tuning system in which the octave is divided into 12 equal semitones, each a factor of 2^(1/12) apart in frequency. This means each semitone is approximately 1.0595 times the frequency of the one below it. Equal temperament makes it possible to play in any key on a fixed-pitch instrument like a piano without retuning, at the cost of slight detuning from pure harmonic intervals. The formula freq = 440 x 2^((n-49)/12), where n is the piano key number (A4 = key 49), gives the frequency of any key in equal temperament.

MIDI (Musical Instrument Digital Interface) is a protocol that represents notes as integers from 0 to 127. The MIDI note number for piano key n is n + 20, because piano key 1 (A0) corresponds to MIDI note 21. Middle C (C4) is piano key 40 and MIDI note 60. The highest piano key (C8, key 88) is MIDI note 108. MIDI note numbers are used in digital audio workstations, synthesizers, and notation software to specify pitches in a hardware-independent way.

The wavelength of a sound wave is the speed of sound divided by the frequency. At room temperature (approximately 20 degrees C), the speed of sound in air is about 343 m/s. Middle C (C4, approximately 261.63 Hz) has a wavelength of 343 / 261.63 = 1.31 metres. The lowest piano note (A0, 27.50 Hz) has a wavelength of about 12.47 metres, which is why bass frequencies are more difficult to absorb with acoustic treatment and require large rooms for accurate reproduction. The highest piano note (C8, 4186.01 Hz) has a wavelength of about 0.082 metres (8.2 cm).

Transposing instruments are notated at a different pitch than they sound. A B-flat clarinet, for example, sounds a major second (2 semitones) lower than written. When a clarinet player reads a C, the instrument sounds B-flat. This means the written frequency in the part is different from the concert frequency. A pianist playing the same concert pitch as a B-flat clarinet reads their note 2 semitones lower in written pitch. This calculator shows concert pitch frequencies. For transposing instruments, add or subtract the appropriate semitone offset to find the written pitch corresponding to a given concert frequency.