Piano Key Frequency Finder – Note to Hz & MIDI Number

Piano key frequencies are calculated using equal temperament tuning based on the formula:
f = A4 × 2(n − 69) / 12
Where A4 = 440 Hz (standard reference), and n is the MIDI note number. Each semitone step multiplies or divides the frequency by the 12th root of 2 (≈1.059463). This ensures that an octave (12 semitones) exactly doubles the frequency.

Middle C (C4) has MIDI note number 60. In the MIDI standard, note numbers range from 0 to 127, where 0 is C−1 (about 8.18 Hz) and 127 is G9 (about 12,544 Hz). A standard 88-key piano spans MIDI notes 21 (A0) through 108 (C8). Middle C at MIDI 60 sits right in the center of the piano keyboard.

A4 = 440 Hz (also called A440 or Stuttgart pitch) was standardized internationally by the ISO in 1975 (ISO 16). Before this, tuning varied widely — Baroque ensembles often used A4 ≈ 415 Hz, while some 19th-century orchestras tuned as high as 456 Hz. Today, 440 Hz is the nearly universal standard, though some orchestras prefer 442 Hz or 443 Hz for a brighter sound. Some alternative tuning communities advocate for 432 Hz, claiming it has a more "natural" resonance, though this is not scientifically substantiated.

A standard full-size piano has 88 keys: 52 white keys and 36 black keys. This spans from A0 (27.5 Hz, MIDI 21) to C8 (4186 Hz, MIDI 108), covering just over 7 octaves. Some larger pianos (like the Bösendorfer Imperial) have up to 97 keys, extending down to C0. Digital keyboards and synthesizers often have fewer keys — common sizes are 61 keys (5 octaves), 76 keys, or 88 keys for full-size digital pianos.

On a modern piano (in equal temperament), C♯ and D♭ are the exact same key — they are enharmonic equivalents. They produce the identical frequency and MIDI number. The choice of name depends on the musical context and key signature. In other tuning systems (like just intonation or microtonal tuning), C♯ and D♭ may actually be slightly different pitches, but on a standard piano they share the same key.

The human hearing range is typically 20 Hz to 20,000 Hz (20 kHz). An 88-key piano covers about 27.5 Hz (A0) to 4,186 Hz (C8), which fits comfortably within the most sensitive part of human hearing. The fundamental frequencies of a piano are all below 5 kHz, but the harmonics (overtones) can extend well beyond 20 kHz, contributing to the instrument's rich timbre. With age, most adults lose sensitivity above 15–17 kHz.

An octave is the interval between one note and another with twice (or half) its frequency. For example, A4 is 440 Hz, and A5 is 880 Hz — exactly double. This 2:1 frequency ratio is perceived as the "same note, but higher" across virtually all human cultures. The term "octave" comes from the Latin octavus (eighth), because in Western diatonic scales, the eighth scale degree is the octave of the first. In equal temperament, an octave is divided into 12 equal semitones.

The MIDI (Musical Instrument Digital Interface) standard assigns a unique number from 0 to 127 to each semitone. MIDI note 69 = A4 (440 Hz) is the anchor point. The formula is: MIDI = 69 + 12 × log2(f / 440). For an 88-key piano: the lowest key A0 = MIDI 21, middle C (C4) = MIDI 60, and the highest key C8 = MIDI 108. MIDI numbers are widely used in digital audio workstations (DAWs), synthesizers, and music software to identify notes unambiguously.