Lower the action by adjusting the bridge, nut, or neck relief
Action — the distance between the strings and the fretboard — is lowered on an acoustic guitar by removing material from the bridge, the nut, or both. The bridge sits at the body end of the strings; the nut sits at the headstock end. Lowering action at the bridge is the most common fix and can be done by sanding the bridge base or shimming it downward. Lowering action at the nut requires filing the nut slots, which is more delicate work. You can also address neck relief — a slight forward bow in the neck — which affects how high the strings sit across the entire fretboard.
Most players start with the bridge because it is the easiest adjustment and covers the majority of action problems. If the bridge is already very low and the strings still sit too high, the nut may need work. If lowering the bridge causes fret buzz, the neck may need a truss rod adjustment or the frets may need leveling — both jobs best left to a technician.
Key Takeaways
- Action is measured at the 12th fret and is lowered by sanding the bridge base, shimming the bridge, or filing the nut slots.
- Sanding the bridge is the safest starting point because you can remove material gradually and stop when the action feels right.
- The nut requires careful filing and is harder to undo, so most players address the bridge first.
- If lowering the bridge causes fret buzz across the board, the neck may have too much relief and needs a truss rod adjustment from a technician.
- Action height varies by player preference, but 2.0 mm at the bass side and 1.75 mm at the treble side is a common target for acoustic guitars.
Measure your current action before you start
Use a ruler or a dedicated action gauge to measure the string height at the 12th fret. Place the ruler flat against the frets and measure the gap between the top of the fret and the bottom of the string. Measure both the bass side (low E string) and the treble side (high E string) because they often differ. Write down both numbers so you know how much material you need to remove.
Most acoustic guitars ship with action around 2.5 to 3.0 mm on the bass side. Many players find 2.0 mm or lower more comfortable for fretting, though some prefer higher action for fingerstyle or to avoid buzz. Your target depends on your playing style and tolerance for buzz, so decide on a goal before you sand.
Sand the bridge base to lower action gradually
The bridge base — the flat surface that sits on the guitar body — is the easiest place to remove material. Lay 120-grit sandpaper on a flat surface (a tile, a glass plate, or a sanding block works well) and sand the bridge base in long, even strokes. Sand the entire base evenly so it stays parallel to the body. Check your progress every few passes by measuring the action again.
Remove only 1 to 2 mm at a time. Once you have sanded, you cannot add material back, so work slowly. After each small reduction, reinstall the bridge and measure the action. Stop when you reach your target. If you sand too much and the action becomes too low, you will need to shim the bridge or replace it entirely.
After sanding, clean any dust from the bridge base and the guitar body, then reglue the bridge using hide glue or a two-part epoxy designed for guitar work. Clamp it firmly and let it cure for 24 hours before stringing the guitar.
Shim the bridge if you need a smaller adjustment
A shim — a thin piece of wood or plastic — can be glued under the bridge to raise it, or removed from under the bridge to lower it. If you have already sanded the bridge and the action is still slightly too high, you can remove a thin shim instead of sanding further. This gives you finer control over the final height.
Shims are typically made from hardwood veneer or plastic and range from 0.5 mm to 2 mm thick. Unglue the bridge carefully using a heat gun or by soaking the joint with water, remove the old shim if one exists, and glue a thinner shim in its place. This method is reversible — you can always add a thicker shim later if needed.
File the nut slots if the bridge is already low
If the bridge is already close to the body and the action is still too high, the nut may be the problem. The nut slots — the grooves that hold each string — can be filed lower to reduce action at the headstock end. This is more difficult than bridge work because the slots must be filed at the correct angle and depth, and mistakes are hard to undo.
Use a nut file set (available from guitar supply shops) that matches your string gauges. File each slot slowly and check the string height frequently. The slot should be just deep enough that the string sits in it without rattling. If you file too deep, the string will buzz against the fret below the nut, and you will need a new nut.
Many players send the nut to a technician for this work rather than doing it themselves. A technician has the right files, the experience to match the slot angle to your bridge, and the ability to replace the nut if something goes wrong.
Check for fret buzz and neck relief after lowering action
After you lower the action, play the guitar and listen for buzz — a rattling sound when you fret a note. Buzz usually means the strings are hitting frets they should not touch. Light buzz on the first few frets is common and often acceptable, but buzz across the entire fretboard suggests a problem with neck relief.
Neck relief is the slight forward bow in the neck that allows strings to clear the frets. If the neck has too much relief (too much bow), lowering the bridge will eventually cause buzz. If the neck has too little relief (too straight or back-bowed), the strings will buzz no matter how high the bridge is. Checking and adjusting neck relief requires a truss rod adjustment, which is best done by a technician with the right tools and experience.
Know when to stop and call a technician
If you have sanded the bridge to near the body and the action is still too high, or if lowering the bridge causes widespread fret buzz, the problem is likely in the neck or frets. Frets can wear unevenly over time, and a worn fret can cause buzz even if the action is low everywhere else. A technician can level the frets, adjust the truss rod, and replace the nut or bridge if needed.
Neck work and fret leveling require specialized tools and experience. The cost of a professional setup — typically $75 to $150 — is worth it if you are unsure about your own work or if the guitar has structural issues. A bad adjustment can damage the guitar or make it unplayable.
Frequently Asked Questions
What is the ideal action height for an acoustic guitar?
Most players aim for 2.0 mm on the bass side and 1.75 mm on the treble side at the 12th fret, though this varies by playing style. Fingerstyle players often prefer slightly higher action to avoid buzz, while strummers may prefer lower action for comfort. Your ideal height depends on your tolerance for buzz and your playing technique.
Can I lower the action without removing the strings?
You can measure and plan without removing strings, but you will need to remove them to sand the bridge or file the nut. Removing strings also lets you clean the fretboard and inspect the bridge and nut for damage. Restring the guitar after your adjustments are complete.
What happens if I sand the bridge too much?
If you sand the bridge base too low, the action will be too low and the strings may buzz against the frets. You can glue a shim under the bridge to raise it slightly, but if the bridge is damaged or warped, you will need to replace it. This is why sanding slowly and measuring frequently is important.
Do I need special tools to lower action?
For bridge work, you need sandpaper, a flat surface, a ruler or action gauge, and glue. For nut work, you need nut files, which are inexpensive but require skill to use correctly. A heat gun or water helps remove the bridge without damage. Most other adjustments require tools and experience that a technician has.
Will lowering the action damage my guitar?
Careful bridge sanding does not damage the guitar if you work slowly and measure as you go. Aggressive sanding or filing can damage the bridge, nut, or frets. If you are unsure about your technique, a professional setup is safer and often costs less than fixing a mistake.