Online Harmonica Tuner

Twenty reeds, none of which you can adjust while playing

A ten-hole diatonic harmonica has twenty reeds — one that sounds when you blow into a hole and a second that sounds when you draw. There is no peg, no slide, no barrel and no tuning screw anywhere on the instrument. Every pitch was filed into a strip of brass at the factory, which means this dial is not here to help you tune the harmonica. It is here to tell you what your harmonica is actually doing: whether a reed has drifted, how far your bends are landing from the note you meant, and whether the reading that looks wrong is a fault or the design.

The layout below is Richter tuning in the key of C, the arrangement used by the overwhelming majority of diatonic harmonicas. Two things about it explain most of what players find confusing. The blow reeds spell a C major chord repeating over three octaves, so any combination of blow holes is a chord. The draw reeds spell a G dominant seventh — a different chord, built on a different root — which is why the two rows behave so differently under a tuner. And the pattern is not uniform: up to hole 6 the draw note is above the blow note, and from hole 7 upward that flips. That one reversal is why bends move from draw to blow halfway along the instrument.

Why a brand-new harmonica reads out of tune

This is the single most common harmonica question, and the answer is that a factory harmonica is deliberately not at A=440 equal temperament. Three separate things push the reading, and they stack.

1. It is tuned sharp on purpose. Blowing or drawing hard drags a reed flat. Rather than let the instrument go flat the moment anyone plays it with conviction, makers tune above concert pitch: Hohner diatonics are set around A=442at moderate breath, so that they still sit near 440 at full volume. Measured gently against a tuner set to 440, the whole instrument therefore reads a few cents sharp. Set concert A to 442 in this tuner’s settings and it reads centred.

2. The thirds and sevenths are flat on purpose. Harmonicas are chord instruments, and a chord only locks together beat-free if its notes follow the small whole-number ratios of just intonation rather than the compromise grid of equal temperament. Those ratios are not opinions — they are arithmetic, and they are what the offsets in the table below are:

Apply those to the two chords and you get the pattern people actually see on a tuner. On a C harp the blow reeds are a C chord, so every E reads about 14 cents flat and every G about 2 cents sharp. The draw reeds are a G7 chord measured against a different root, so every B reads about 14 cents flat — and 5 draw, the seventh, reads about 31 cents flat, which is the outlier that sends people reaching for a file.

That table is full just intonation — the recipe Hohner used on Marine Bands before the mid-1970s. Most harmonicas made today use a compromise tuningthat sits partway between it and equal temperament, so expect your instrument to show the same shape with smaller numbers. Models built for melody playing, notably the Hohner Golden Melody, go the other way and ship in straight equal temperament, where every column above reads zero. Your harmonica’s model page or manual is the authority on which it is.

3. Your breath is moving the reading. Reed pitch depends on how hard you drive it, and the effect is large enough to swamp everything else on this page. A gentle breath reads sharp; leaning into the note reads flat.

Bends: what a tuner is genuinely good for here

A bend is not a separate reed. When both reeds in a hole are made to interact, the pitch drops into the gap between them — which means the depth of a bend is set by how far apart that hole’s two reeds are, and nothing else. A hole whose reeds are three semitones apart gives you two bent notes; a hole whose reeds are a semitone apart gives you none worth naming. That single rule generates the entire bend map, and it explains the two facts every beginner trips over: why hole 3 is the richest hole on the instrument, and why hole 5 refuses to bend.

Because a bend is placed entirely by the shape of your mouth and throat, with nothing to stop it at the right point, the usual failure mode is landing between two notes and not being able to hear it. That is exactly what a dial fixes. Play the bend, hold it steady, and check that the tuner names the note you were aiming for and settles rather than sagging. The bends worth drilling first are the three under hole 3 — the whole-tone one lands on concert A, which makes it trivially easy to check, and the tone-and-a-half bend below it is the deepest and least reliable note on the instrument.

Which key of harmonica do you need?

A diatonic harmonica plays one key comfortably, so players own several and choose by song. Which one you pick depends on the position you play in. First position, or straight harp, takes a harmonica in the same key as the song and lives on the blow reeds — bright, major, folk. Second position, or cross harp, takes a harmonica a perfect fifth below the song, puts the tune on the draw reeds where the bends are, and is what almost all blues is played in. Third position sits a whole tone below and gives a minor, Dorian sound.

If you only ever buy one, buy a C harmonica — it is the key almost every tutorial and tab is written for, and it plays cross harp in G, the most common key in blues and folk. A second harp in A (cross harp in E) covers most of what is left.

How a harmonica’s pitch is actually changed

By removing metal from the reed. There is no other mechanism, and the direction is not intuitive: filing near the free tip raises the pitch, because the tip is the part with the most movement and taking mass off it lets the reed vibrate faster. Filing near the riveted base lowers the pitch, because that thins the part of the reed that does the bending, effectively softening its spring. Manufacturer instructions from both Hohner and Seydel describe the same two operations.

Two details matter more than technique. File along the reed rather than across it — cross-scratches concentrate stress and are a known cause of reeds cracking early. And work in tiny passes, checking after each one, because none of it can be undone: material removed is gone, and a reed filed past its target can only be brought back by removing more metal somewhere else, which shortens its life every time. Reeds also read flatter when warm, so a plate that has just come out of your hands or a warm mouth will not measure the same as a cold one.

Checking a harmonica, step by step

1. Decide your reference pitch first.A=440 if you play with fixed-pitch instruments and want to know your true offset; A=442 if you want to see how close your harmonica is to how its maker intended it. Set it in this tuner’s settings before you play anything.
2. Warm the harmonica up by cupping it or playing gently for a minute. Cold reeds read sharp of where they will sit in use, so a cold measurement is not the one you want to act on.
3. Work through the blow row first, hole 1 to 10, then the draw row. Doing one row at a time is what makes the pattern visible — a whole row sitting a few cents sharp is a reference-pitch story, one reed alone out of step is a reed story.
4. Play each note single, steady and at normal volume, and read the sustain, not the attack. Write the cents figure down rather than trusting memory across twenty reeds.
5. Compare against the pattern, not against zero. Thirds low, fifths a touch high, 5 draw well low — that is a healthy just or compromise tuning. An E that sits 30 cents flat when the other two E reeds sit at 14 is the one to investigate.
6. Then check your bends using the bends tab above, one hole at a time, holding each bend long enough for the dial to settle.

Chromatic and tremolo harmonicas

A chromatic harmonica works differently enough to change your expectations. A button-operated slide swaps in a second set of reeds a semitone higher, so all twelve notes are available and there is no need to own one instrument per key. Because it is played as a melody instrument rather than a chord instrument, a chromatic is normally tuned in or very close to equal temperament — meaning it genuinely should read near zero across the board, and a flat third is a fault rather than a feature. It also has twice as many reeds, so check both slide-in and slide-out for every hole.

A tremolo harmonica is the opposite case, and the one most likely to confuse a tuner. It carries two reeds per note, deliberately tuned slightly apart so their beating produces the wavering sound the instrument is named for. A dial fed two close frequencies at once will waver or refuse to settle, and that is the instrument working correctly. Judge a tremolo by the steadiness and speed of its beat rather than by a cents readout, exactly as you would the musette ranks on an accordion.

Equal temperament, and what this dial can and cannot tell you

Like every chromatic tuner, this one measures against twelve-tone equal temperament — the grid a piano uses. For a harmonica that makes it an excellent instrument for spotting a drifted or cracked reed, for measuring how far your bends land from their targets, and for finding out where your instrument sits relative to concert pitch. It makes it a poor judge of whether the harmonica is correctly tuned, because most harmonicas are intentionally not on that grid.

The useful habit is to read the dial for pattern and consistency rather than for zeroes. If you want to understand why an interval can be measurably off the grid and still be the more in-tune-sounding choice, our guide to cents covers the arithmetic behind the offsets in the table above.

Frequently asked questions