Chord Frequency Calculator

Every note in a chord is a sound wave at a precise frequency, and the character of the chord comes from how those frequencies relate to each other. This calculator gives you the frequency of each note, and then shows the part most tuning discussions skip: how far the piano you are playing sits from the pure ratios your ear is actually listening for.

Frequency of any note

f = A4 × 2^(n/12)

• A4 is the tuning reference, 440 Hz by international standard (ISO 16) since 1939
• n is the number of semitones above (+) or below (−) that A4
• 2^(1/12) ≈ 1.05946 is the ratio between adjacent semitones in equal temperament

That single formula produces every note. Middle C (C4) is 9 semitones below A4, so 440 × 2^(−9/12) = 261.63 Hz. The lowest piano key, A0, is 27.5 Hz. The highest, C8, is 4,186.01 Hz.

Equal temperament against just intonation

Take a C major chord in the fourth octave. In equal temperament the calculator returns C4 = 261.63 Hz, E4 = 329.63 Hz, G4 = 392.00 Hz.

Now take the ratios your ear wants. A pure major third is exactly 5:4 and a pure fifth exactly 3:2, giving 4:5:6 across the triad. From the same C4:

The fifth is close enough that almost nobody hears the difference. The third is not. Every major third on a piano is about a seventh of a semitone sharp of pure, and if you sustain that C and E against a justly-tuned reference you can count the beats: 329.63 − 327.03 is roughly 2.6 beats per second.

This is the bargain equal temperament makes. Bending every interval slightly out of tune is what lets one instrument play in all twelve keys without retuning. String quartets and barbershop singers, who have no frets to argue with, drift back toward the pure ratios on their own.

Concert pitch is not fixed

The A4 reference is a convention, not a constant, so the calculator lets you change it:

• 440 Hz is the international standard
• 442–444 Hz is common in European orchestras, which prefer the brighter edge
• 432 Hz has a following among some musicians
• 415 Hz is the usual choice for Baroque repertoire, almost exactly a semitone below modern pitch

Change the reference and every frequency shifts with it, but the ratios between the notes of the chord never move. That is why a piece transposed to Baroque pitch still sounds like itself.