What Is a Cent in Music? How to Read Your Tuner

100 cents in a semitone

A cent is a unit for measuring the distance between two pitches. By definition, one equal-tempered semitone, the step between two neighboring keys on a piano, is 100 cents. An octave contains twelve semitones, so it’s 1,200 cents.

So when your tuner shows “+20,” you’re 20 cents sharp: one fifth of a semitone above the target. At “−50” you’re half a semitone flat, right between the target note and the note below it. Past 50 cents you’re actually closer to the neighboring note. That’s why our tuner, in chromatic mode, always shows the nearest note name and uses the needle only for the ±50 cents around it.

The big advantage of cents is that they mean the same thing everywhere on the keyboard. “Ten cents sharp” is the same amount out of tune on a low bass string as on a high violin note.

Cents vs hertz

Hertz (Hz) counts vibrations per second. A difference in cents turns into a different number of hertz depending on how high the note is: the higher the note, the more hertz a cent covers. With A4 = 440 Hz, here’s what 5 cents means at a few pitches:

• Bass low E1 (about 41.2 Hz): 5 cents ≈ 0.12 Hz
• Guitar low E2 (about 82.4 Hz): 5 cents ≈ 0.24 Hz
• A4 (440 Hz): 5 cents ≈ 1.27 Hz
• A5 (880 Hz): 5 cents ≈ 2.55 Hz

That’s why “off by 1 Hz” can mean very different things. On a high note it’s tiny. On a bass E1, 1 Hz is more than 40 cents, almost half a semitone. Tuners show cents front and center for exactly this reason.

How many cents can you hear?

The smallest pitch difference a person can detect is called the just-noticeable difference (JND). The honest answer is that there isn’t one fixed number. It depends on how high and how loud the notes are, their timbre, how trained the listener is, and how the test is done.

• Many references treat about 5 cents as a typical threshold.
• Under the most sensitive conditions, around 2,000 Hz at a comfortable level, one review puts it at about 3 cents, and some trained musicians can do even better.
• A difference of a single cent, on the other hand, is generally too small to notice between two notes played one after the other.

It also matters whether you hear the notes one after another or together. Two notes that are slightly apart, sounded at the same time, produce a pulsing “wah-wah” called beating. The beat rate equals the difference in frequency, so 440 Hz and 442 Hz beat twice per second. Beating exposes small differences that you’d miss when hearing the notes separately, which is why a tuning that sounds fine solo can bother you in a group.

What “in tune” means on a tuner

Our tuner turns the needle green and shows “in tune” when you’re within ±5 cents of the target, inclusive. As described above, about 5 cents is the figure many references give as the edge of what people can tell apart.

When you’re practicing on your own, landing in the green zone is good enough to move on to the next string. If you’re playing with others and still hear beating, try to bring the needle closer to zero. As you get closer, the beats get slower and slower until you can hardly notice them.

Equal temperament vs just intonation in cents

Cents are also the easiest way to compare tuning systems. Pianos and nearly all tuners use equal temperament, which splits the octave into twelve identical semitones of 100 cents. A major third is 400 cents and a perfect fifth is 700 cents.

Just intonation instead tunes intervals to simple whole-number frequency ratios, and the numbers come out a little different:

• Major third (5:4): about 386.3 cents, roughly 14 cents narrower than equal temperament
• Perfect fifth (3:2): about 702.0 cents, roughly 2 cents wider
• Minor third (6:5): about 315.6 cents, roughly 16 cents wider

A 2-cent difference in the fifth is below the thresholds above, but the roughly 14-cent gap in the major third, about a seventh of a semitone, is well above the 5-cent figure. In groups that hold long chords, the difference between the two systems can come through. Since our tuner works in equal temperament, use it to get each note in place, then listen to how the chord itself rings.