Why guitars go out of tune

Quick diagnosis

Match what you notice to the likely cause, then read that section.

• Keeps going flat for days after a restring: the strings are still stretching.
• Out of tune after moving between rooms, or overnight: temperature or humidity.
• Drops suddenly, sometimes with a ping: a string slipping at the post or ball end, or catching in the nut.
• Clicks or pings while you tune, and the pitch jumps in steps: nut binding.
• Off after using the tremolo arm or a big bend: friction at the nut, string trees or bridge, or an unbalanced floating tremolo.
• Open strings in tune, but chords up the neck sound wrong: intonation, finger pressure or the capo.
• Action and buzzing change with the seasons: neck relief.

Before blaming the guitar, make sure you finish each string by tuning up to the note, as described in how to tune a guitar. Tuning down to a note leaves slack that lets the string slip flat later, and it looks exactly like a hardware problem.

New strings stretching

A new string lengthens slightly under tension during its first hours on the guitar. At the same time, the wraps around the tuning post pull tighter and the ball end settles into its seat. Each of those lets the string go flat.

Fix: tune to pitch, then hook a finger under each string and pull it gently away from the fretboard, moving along its length. Retune and repeat. After three or four rounds the pitch stops dropping. Expect to touch up the tuning more often than usual for the first day or two of playing anyway. Nylon strings on classical guitars stretch far more than steel and can take several days to settle.

Temperature

Steel strings expand when they warm up. Because the string is fixed at both ends, that expansion lowers its tension and the pitch goes flat. When it cools, it goes sharp. Strings react within minutes; the wooden neck and body follow much more slowly. Stage lights, sun through a window, a cold car and even the heat of your body over a long set all shift the tuning.

Fix: let the guitar reach room temperature before you tune it. When you bring it in from the cold, leave it in its case for a while first, which also protects the finish from sudden temperature changes. On a hot stage, check the tuning between songs, not just at the start. Never leave a guitar in a parked car.

Humidity

Wood absorbs moisture from the air and releases it again over hours to days. Acoustic guitars, with their thin tops, react the most. In humid weather the top swells and lifts the bridge, the action rises and the pitch usually creeps sharp. In dry weather the reverse happens: the action drops, strings may buzz, pitch tends to go flat, and in long dry spells the fret ends can start to stick out from the edge of the fretboard and the top can crack.

Fix: keep the guitar somewhere stable, away from heaters, air conditioning vents and outside walls. Many acoustic makers recommend moderate humidity, roughly 45 to 55 percent relative humidity. A small hygrometer in the case tells you where you are, and a case humidifier helps in dry seasons. Expect to retune more often when the weather changes.

Strings slipping at the post or the ball end

At the post. With too few wraps, a string can creep around the post, especially a plain unwound string. Leave enough slack for a couple of wraps on wound strings and a few more on plain ones, and wind them downward so the string leaves the post low. On slotted vintage-style posts, push the string end into the center hole before winding. A locking wrap, where the string passes under itself on the first turn, also holds well, and locking tuners clamp the string so it cannot slip at all.

At the ball end. On an acoustic with bridge pins, the ball end can hang on the tip of the pin instead of sitting against the bridge plate inside the guitar. When it finally slips into place, the string drops flat. When restringing, push the pin down and pull the string up gently until you feel the ball seat, then tune. On electrics, the small wrap of wire at the ball end can tighten during the first hours, which is one more reason to stretch new strings.

Nut binding

The nut slot has to guide the string without gripping it. If a slot is too narrow, rough or pinches the string, the string moves through it in jerks. You hear a ping or click while tuning, the pitch jumps instead of moving smoothly, and after a bend the string stays sharp until something knocks it loose. Binding often starts when you change to heavier strings than the nut was cut for.

Fix: lubricate the slots every time you change strings. If a string still binds, a guitar tech can widen or polish the slot. Do not file it yourself without experience. A slot cut too deep makes the string buzz, and the usual cure for that is a new nut.

Tremolo systems

A floating tremolo balances the pull of the strings against springs in the back of the guitar. Change the tension of one string and the bridge moves, which changes all the others. That has three consequences:

• Tuning one string slightly detunes the rest, so you need several passes. HeyTuner’s checklist ends with a recheck pass for this reason.
• Bending one string pulls the bridge forward and the other strings go flat while you bend. You hear it when you bend one note against another one that is ringing.
• After using the arm, strings can catch at the nut, the string trees or the bridge pivots and come back a few cents off.

Fixes: lubricate the nut and string trees, use enough wraps or locking tuners, and stretch new strings thoroughly. Keep the bridge pivot points clean and undamaged. On a double-locking system, tune, lock the nut, then use the fine tuners only. After tuning, push the arm down gently and let it return: if the strings move, friction is still holding something. If you never use the arm, tighten the springs until the bridge rests on the body, or have it blocked. The guitar then stays in tune like a fixed bridge.

Playing hard and bending

Pressing harder than needed pushes a fretted note sharp, especially on tall frets and light strings. A hard pick attack starts sharp too. Big bends drag the string through the nut and over the saddle, and if either one grips, the string does not fully return.

Fixes: press just hard enough for a clean note. If one string goes off after bends, look at its nut slot. Capos cause the same problem: a capo clamped too hard, or placed far from the fret, pulls the strings sharp. Place it just behind the fret, with only as much pressure as it needs, and retune with it on if the song needs precision.

Neck relief changes

String tension bows the neck forward slightly, and the truss rod inside counters that pull. The small forward bow that remains is called relief. It changes with the seasons, with humidity and whenever you change string gauge or tuning. More relief raises the action in the middle of the neck, which makes fretted notes there go sharper. Less relief makes the strings buzz.

Fix: a truss rod adjustment, made in small turns of an eighth to a quarter of a turn, giving the neck time to settle between adjustments. Never force a rod that will not turn. If you have not adjusted one before, a tech will do it as part of a setup.

Intonation versus tuning

Tuning gets the open strings to the right pitch. Intonation is whether the fretted notes are right too. When you press a string to a fret, you stretch it slightly, and that raises the pitch. The saddle sits a little further back than the exact mathematical position to make up for this. That extra length is called compensation, and it has to suit your string gauge, action and tuning.

That is why a guitar tuned perfectly open can sound wrong up the neck. To check:

1. Tune the string open.
2. Fret it at the 12th fret and read the tuner.
3. If the fretted note is sharp, the string is too short: move the saddle back, away from the neck.
4. If it is flat, the string is too long: move the saddle forward, toward the neck.
5. Retune open and check again. Repeat until both readings match.

Electric guitars usually have a screw for each saddle. Acoustic saddles are fixed, so correcting them is a job for a tech. Old strings intonate badly however well the saddle is set, so put on fresh strings before you adjust anything.

Two more effects are normal and not faults. A nut slot cut a little high makes the first few frets sharp. Equal temperament is a compromise: its major thirds are about 14 cents wider than acoustically pure ones, so some chords sound slightly rough even on a perfectly set-up guitar. Tuning one string to sweeten one chord makes other chords worse.

Loose hardware

A tuning machine whose bushing nut or mounting screw has worked loose can rock under tension and drift. Check that each tuner feels firm and that the bushing nuts on the face of the headstock are snug. Tighten them gently, as overtightening can crack the finish. On electrics, check that the bridge and tailpiece are not tilting or moving.

When to take it to a tech

Book a setup when the guitar still drifts after you have stretched the strings, lubricated the nut and checked the post wraps, when you change string gauge or settle into a different tuning, when the action or buzzing changes noticeably, or when intonation is off and you cannot adjust it yourself. A setup covers relief, action, nut slots and intonation together, which is how those problems are best fixed. If you change tunings often, read changing tunings safely first.