Note Frequency Calculator
Calculate note frequency from the published formulas and tables for the craft.
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What this tool does
Calculate note frequency from the published formulas and tables for the craft. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
How to use the Note Frequency Calculator
- Enter or select semitones from a4 (0 = a4, +3 = c5, −9 = c4).
- Enter or select frequency to identify (hz).
- Read the calculated result; change any measurement to compare alternatives.
Formula
equal temperament with A4 = 440 Hz: frequency = 440 × 2^(semitones from A4 ÷ 12); nearest note to a frequency: MIDI = round(69 + 12 × log2(frequency ÷ 440)); cents deviation = 1200 × log2(frequency ÷ nearest note frequency)
- semitones
- Semitones from A4 (0 = A4, +3 = C5, −9 = C4)
- frequency
- Frequency to identify (Hz)
Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
Worked example
For note frequency calculator, the following measurements illustrate the exact method: Semitones from A4 (0 = A4, +3 = C5, −9 = C4): 0; Frequency to identify (Hz): 440.
Inputs
- Semitones from A4 (0 = A4, +3 = C5, −9 = C4)0
- Frequency to identify (Hz)440
Result
- Frequency (Hz)440
- Note nameA4
- Nearest note to entered frequencyA4
- Nearest note frequency (Hz)440
- Cents deviation from nearest note0
Results explained
- Frequency (Hz)
- Frequency (Hz) from the formula above. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
- Note name
- Note name from the formula above. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
- Nearest note to entered frequency
- Nearest note to entered frequency from the formula above. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
- Nearest note frequency (Hz)
- Nearest note frequency (Hz) from the formula above. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
- Cents deviation from nearest note
- Cents deviation from nearest note from the formula above. Twelve-tone equal temperament referenced to A4 = 440 Hz (ISO 16). Orchestras that tune to A442 or A443 and historical temperaments will differ slightly.
Frequently asked questions
A4 is 440 Hz by international standard. Every semitone multiplies frequency by 2^(1/12) ≈ 1.0595, so a note n semitones from A4 is 440 × 2^(n/12) Hz. C5 is 3 semitones above A4: 440 × 2^(3/12) ≈ 523.25 Hz.
Round 69 + 12 × log2(frequency ÷ 440) to the nearest MIDI number and read off the note. 466 Hz lands on A#4/Bb4 (466.16 Hz) within a cent or two — this calculator also reports the exact cents deviation from the nearest equal-tempered note.
A cent is one hundredth of a semitone: 1200 × log2(your frequency ÷ the target note's frequency). Within about ±5 cents most listeners hear a note as in tune; ±10–15 cents is noticeable in sustained chords.
Equal temperament divides the octave's 2:1 frequency ratio into 12 equal multiplicative steps, so 12 semitones always multiply frequency by exactly 2. A3 is 220 Hz, A4 is 440 Hz and A5 is 880 Hz.
It is the ISO 16 standard and the default for tuners and synths, but some orchestras tune to A442–A444 and period ensembles use A415 (about a semitone flat). This calculator fixes A4 = 440 Hz; shift every result proportionally for another reference.