Note Frequency Calculator

About This Tool

The Note Frequency Calculator converts any musical note to its precise frequency in hertz (Hz). It uses equal temperament tuning with a configurable concert pitch (default A4 = 440 Hz) and supports cents-level fine adjustments for non-standard tunings. Pick a note and octave, optionally tweak the A4 reference or add cents, and you get the frequency, MIDI number, wave period, and physical wavelength.

The Math Behind the Frequency

Equal temperament divides every octave into 12 equal semitones. Mathematically, each semitone is a frequency ratio of the twelfth root of two (about 1.05946). The formula for any note's frequency, using A4 as the anchor, is: frequency = A4 × 2^((MIDI_number − 69) / 12). MIDI 69 is A4. MIDI 60 is middle C. Subtract 12 to drop an octave; add 12 to raise an octave. Each integer step is a semitone.

Common Note Frequencies

A few frequencies worth memorizing: A4 = 440 Hz (concert pitch). C4 (middle C) = 261.63 Hz. E2 (low E on guitar) = 82.41 Hz. E4 (high E on guitar) = 329.63 Hz. The piano's lowest note A0 = 27.5 Hz, and the highest note C8 = 4186 Hz. Human hearing tops out around 20,000 Hz (less for adults), so the upper register of music is mostly perceived through harmonics and overtones rather than fundamental frequency.

Concert Pitch History

Before 1955, A4 was inconsistent. Baroque musicians used 415 Hz (a semitone below modern). Many 18th-century European orchestras tuned to 422 Hz. By the late 19th century, pitches had crept up to 435-460 Hz. ISO 16 standardized A4 = 440 Hz internationally. Some orchestras (especially in Germany and Austria) tune slightly sharp at 442-443 Hz for brilliance. Period instrument groups still use 415 Hz for baroque or 430 Hz for classical-era repertoire.

Cents and Fine Tuning

One cent is 1/100 of a semitone. A trained ear can hear about 5 cents in isolation and 2-3 cents in tuned chords. Synthesizer detuning often uses 5-15 cents to fatten unison voices. The natural just-intonation major 3rd is about 14 cents flat compared to equal temperament. Use the cents field to model these effects: enter ±10 cents to hear what a slightly detuned voice would sound like, or enter −14 to compute a just-tuned major 3rd.

Wavelength and Acoustics

Wavelength is the physical length of one full cycle in air, calculated as speed of sound (≈343 m/s) divided by frequency. Low frequencies have long wavelengths and need physical space to fully develop, which is why subwoofers behave differently in small rooms than large ones. Knowing wavelengths helps with room treatment, speaker placement, and even the design of woodwind and brass instruments.

Pair With Other Tools

Use this calculator alongside our Music Interval Calculator to compute interval ratios, the Chord Progression Builder for harmonic context, the Circle of Fifths Tool for key relationships, the Tap Tempo BPM for finding song tempos, or the BPM to Delay Calculator for tempo-synced effects.