Frequency formula: f = A4 × 2^((n − 69) / 12), where n is the MIDI note number. A4 defaults to 440 Hz standard concert pitch. Related: note frequency, cents to frequency, equal temperament.
You select a note from C2 to C7 and optionally adjust the A4 reference frequency. The tool converts the note to a MIDI number, calculates the semitone distance from A4, then applies the equal temperament formula: frequency = A4 × 2^((n − 69) / 12). The default 440 Hz reference matches ISO 16 standard concert pitch.
The International Organization for Standardization adopted 440 Hz as concert pitch in 1955 (ISO 16). While some orchestras tune slightly higher (e.g., 442 or 443 Hz), 440 Hz remains the most widely used reference worldwide.
Equal temperament divides the octave into 12 equal semitones, each with a frequency ratio of 2^(1/12) ≈ 1.05946. This lets instruments play in any key without retuning, though intervals are slightly different from pure (just) intonation.
MIDI assigns each note an integer from 0 to 127. Middle C (C4) is MIDI 60, and A4 is MIDI 69. Each semitone up adds 1. This numbering is used universally in digital audio and music software.
Yes — adjust the A4 reference field. Baroque ensembles often use 415 Hz, and some modern orchestras use 442–443 Hz. The calculator recalculates all notes relative to whatever reference you set.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.