Note Frequency Calculator

Every musical pitch corresponds to a vibration rate measured in hertz (Hz), or cycles per second. Equal temperament divides each octave into twelve semitones, each a factor of 2^(1/12) apart. That exponential spacing is why A4 at 440 Hz doubles to 880 Hz at A5 — one octave — and why semitone steps multiply frequency by 2^(1/12) ≈ 1.05946. Concert pitch sets A4 as the reference; all other notes derive from that anchor.

Enter a note name like C4, F#5, or Bb3 in Note → Hz mode. Accidentals use # for sharp or b for flat immediately after the letter. The calculator returns frequency in Hz plus the period in milliseconds — how long one wave cycle takes. In Hz → Note mode, type a measured frequency and get the nearest note name, useful when tuning instruments from a spectrum analyzer or calibrating oscillators.

The A4 reference field defaults to 440 Hz, the modern ISO standard. Baroque ensembles sometimes use A = 415 Hz; some orchestras tune to 442–443 Hz for brightness. Changing the A4 reference shifts every computed note together — it does not change the interval between notes, only the absolute Hz values. Historical pitch and microtonal work often starts by adjusting this field.

Worked example with the default fields: note A4 and A4 reference 440 Hz. The frequency is exactly 440 Hz — the tuning fork standard. The period row shows about 2.27 ms per cycle (1000 ÷ 440). Switch to Hz → Note with 440 Hz entered and you get A4 back. Try 466 Hz and the nearest note is A#4 — one semitone above concert A.

Middle C (C4) lands near 261.63 Hz at A4 = 440. Guitarists often reference the open A string (A2 ≈ 110 Hz) and the harmonic at the twelfth fret. Synthesizer designers use these conversions to set oscillator coarse/fine tuning when the UI shows note names but the engine expects Hz.

Common mistakes include omitting the octave number (A alone is ambiguous — A3 and A4 differ by a factor of two), using flats where the parser expects sharps (Db4 works as written with b, but some tools spell it C#4), and comparing tuner readings without matching the reference pitch. Strobe tuners may display cents offset from equal temperament — pair this tool with the cents calculator for fine adjustments.

MIDI note numbers appear in Hz → Note results as a convenience row. MIDI note 69 is A4 at standard tuning. Sampling rate and anti-aliasing set upper practical limits for digital synthesis, but the math here is continuous — it does not cap Nyquist frequency.

Limits: this calculator uses equal temperament only. Just intonation, Pythagorean tuning, and arbitrary microtonal scales need different formulas. It does not model inharmonic partials of bells or stretched piano tuning. Verify note spelling with your ensemble’s score conventions when switching between transposing instruments.