Note Frequency Calculator
Converts any MIDI note number into its precise pitch frequency in Hz. Essential for synthesizer tuning, audio programming, and understanding the physics of musical pitch.
About this calculator
Every musical pitch corresponds to a specific frequency measured in hertz (Hz). The international standard sets MIDI note 69 (A4) at exactly 440 Hz. From there, each semitone up or down multiplies or divides the frequency by the twelfth root of 2 (²¹²√2 ≈ 1.05946). The formula is: f = 440 × 2^((noteNumber − 69) / 12). MIDI note numbers run from 0 (C−1, ~8.18 Hz) to 127 (G9, ~12,544 Hz), with middle C (C4) at note 60 and approximately 261.63 Hz. This equal-temperament system ensures every octave is an exact 2:1 frequency ratio. Audio engineers, synthesizer developers, and composers use this formula to tune oscillators, design filters, and analyze pitch relationships mathematically.
How to use
Suppose you want the frequency of C4 (middle C), which is MIDI note 60. Enter 60 in the 'MIDI Note Number' field. The calculator computes: f = 440 × 2^((60 − 69) / 12) = 440 × 2^(−9/12) = 440 × 2^(−0.75) = 440 × 0.5946 ≈ 261.63 Hz. This matches the standard tuning of middle C. Try note 69 for exactly 440 Hz (A4), or note 81 for A5 at 880 Hz — one octave higher, exactly double the frequency.
Frequently asked questions
How is MIDI note number related to musical pitch and frequency?
MIDI assigns an integer from 0 to 127 to each semitone across the piano range. Note 69 is A4 at 440 Hz, note 60 is middle C at ~261.63 Hz, and every 12 notes represent one octave. Each step up multiplies the frequency by 2^(1/12) ≈ 1.05946. This system lets computers represent pitch as a simple integer while the formula converts it to a physically meaningful frequency.
Why is 440 Hz used as the standard tuning reference for music?
440 Hz for A4 was adopted as the international standard (ISO 16) in 1955 to ensure consistency across orchestras, recordings, and instruments worldwide. Before standardization, tuning varied significantly between countries and eras — Baroque tuning often used A = 415 Hz. Some orchestras and soloists still use A = 442 or 443 Hz for a slightly brighter sound, but 440 Hz remains the universal default for digital audio and MIDI systems.
What is the frequency difference between two notes one semitone apart?
Two notes one semitone apart differ by a factor of 2^(1/12) ≈ 1.05946, meaning the higher note is about 5.946% higher in frequency. In absolute terms, the gap grows as pitch rises — the semitone between A4 (440 Hz) and A#4 is about 26 Hz, while the same interval an octave higher (A5 to A#5) is roughly 52 Hz. This logarithmic spacing reflects how human hearing perceives equal pitch steps even as absolute frequency differences grow.