Guitar Action Height: mm Chart and Inch Converter

Guitar action height is the gap from the top of a fret to the underside of a string. The number becomes useful when you also record the string, measuring fret, tuning and whether you used a capo. This guide helps you read that gap, convert your ruler's units and choose the right reference before adjusting anything.

Quick Answer: Measure action from the fret crown to the string's underside at your intended tuning. Use the fret and capo method specified by your guitar's maker: Fender's Strat and Tele setup procedures use the 17th fret, while the acoustic starting ranges below use open strings at the 12th fret. 4/64 inch is 1.5875 mm. Converting units does not convert one measuring method into another.

On this page:

• Convert a reading
• String-height conversion chart
• Choose a target and measuring method
• Measure action step by step
• Find the cause before adjusting
• Electric and acoustic adjustment routes
• Keep a repeatable setup record
• Frequently asked questions

Guitar String Height Chart: Inches to mm

This table converts lengths. It does not label a measurement as good or bad for a particular instrument. A reading near 2 mm might be comfortable on one string and unsuitable on another, depending on the instrument, fretwork, tuning and your attack.

The calculation uses the international definition 1 inch = 25.4 mm, documented by NIST. Multiply an inch value by 25.4 to get millimetres. Divide millimetres by 25.4 to get decimal inches.

Ruler marking	Equivalent fraction	Decimal inches	Millimetres, rounded
2/64 inch	1/32 inch	0.03125	0.794 mm
3/64 inch	3/64 inch	0.046875	1.191 mm
4/64 inch	1/16 inch	0.0625	1.588 mm
5/64 inch	5/64 inch	0.078125	1.984 mm
6/64 inch	3/32 inch	0.09375	2.381 mm
7/64 inch	7/64 inch	0.109375	2.778 mm
8/64 inch	1/8 inch	0.125	3.175 mm
9/64 inch	9/64 inch	0.140625	3.572 mm
10/64 inch	5/32 inch	0.15625	3.969 mm

Read fractions without losing the denominator

A mark labelled 4 on a ruler's 64ths scale means 4/64 inch, not four inches or 0.4 inch. In the converter above, select fractional inches and enter the complete fraction. You can enter 1/16 directly; it describes the same length as 4/64.

For example, entering 5/64 produces approximately 1.984 mm. Entering 2 mm produces approximately 5.04/64 inch, whose nearest whole ruler mark is 5/64. Those are close readings, not an instruction to lower a string by their tiny difference.

Separate conversion precision from measuring precision

A calculator can display three decimal places even when your ruler cannot resolve them. If you can only read to about 0.1 mm, record that practical precision. Do not turn a rounded conversion into a claimed change in your guitar's setup.

Choose one unit for your working notes and keep the original reading. Repeatedly rounding a measurement from mm to a whole fraction and back can create a difference that never existed on the instrument. The converter shows the decimal value as well as the approximate ruler mark for this reason.

Choose a Guitar Action Target With the Correct Method

A useful reference gives you more than two numbers. It identifies the guitar or setup type, the measuring fret, the strings, and any capo or fretting instructions. Treat a chart missing those details as incomplete.

Fender electric guitar string-height reference

Fender's Stratocaster setup procedure and Telecaster procedure measure action at the 17th fret, after checking tuning. Their action tables vary with fingerboard radius. Here are those starting references with rounded metric equivalents:

Fender fingerboard radius	Bass side at 17th fret	Treble side at 17th fret
7.25 inches	5/64 inch, about 2.0 mm	4/64 inch, about 1.6 mm
9.5–12 inches	4/64 inch, about 1.6 mm	4/64 inch, about 1.6 mm
15–17 inches	4/64 inch, about 1.6 mm	3/64 inch, about 1.2 mm

These are the cited Fender references, not a universal table for every electric guitar. Follow your model's documentation for unusual bridges, replacement necks or other specifications. Test bends as well as straight fretted notes before settling on an action height.

Do not move these numbers to the 12th fret and call the result Fender's factory setup. The measuring position is part of the specification. Our Stratocaster setup guide connects the action check to the rest of that setup sequence.

For printable Fender setup notes, the guide's coverage and sample are at https://owningafender.com/products/fender-setup-guide. Check the listed coverage against your instrument before buying.

Acoustic guitar string height at the 12th fret in mm

For a conventional six-string steel-string acoustic, roughly 2.4–2.8 mm on the low E and 1.6–2.0 mm on the high E can be practical starting ranges for discussion and testing. These are editorial starting ranges, not universal Martin, Taylor or Yamaha factory specifications.

Measure the open strings at the 12th fret, tuned to your playing pitch, with no capo for this comparison. Do not apply this table to nylon-string guitars, twelve-strings or an instrument whose manufacturer specifies a different procedure.

String	Illustrative 12th-fret starting range	Nearby inch ruler marks
Low E, bass side	2.4–2.8 mm	About 6/64–7/64 inch
High E, treble side	1.6–2.0 mm	About 4/64–5/64 inch

A forceful strummer may need more clearance; a light fingerstyle player may prefer less if the instrument supports it. The goal is comfortable playing with an acceptable response, not the smallest number. Use the acoustic action guide for humidity, relief, nut and saddle checks before changing anything.

Other electrics, basses and specialised setups

Use the actual manufacturer's method for a Les Paul, PRS, bass or other instrument. Scale length alone does not determine a suitable action height. A shared 24.75-inch or 25.5-inch scale is not enough to transfer a setup specification between models.

The setup specs lookup can help locate a model reference. Check its source and measurement notes before comparing. If you only know your own comfortable setup, keeping repeatable measurements of that guitar is still useful; you do not need a universal target to document a change.

How to Measure Guitar Action Height

You need a tuner, a ruler or gauge whose scale starts at its measuring edge, and good light. A household ruler with an unmarked margin before zero will overstate the gap. A capo and feeler gauges are useful for separate relief checks but are not automatically part of every action measurement.

Prepare a repeatable reading

Keep the guitar in its usual playing position without pulling the neck towards you. If you support it on a bench, make sure nothing pushes the neck into a different position. Repeat future measurements in the same position.

Use the string set and tuning you intend to play. If you are changing gauge, finish fitting and tuning the strings before recording the new setup. A reading with slack strings does not describe the instrument under playing tension.

Take and record both outer-string measurements

1. Tune the guitar. Confirm the intended tuning rather than assuming standard tuning.
2. Select the measuring method. Use the maker's specified fret and capo arrangement, or clearly label your own repeatable method.
3. Place the gauge on the fret crown. Read to the underside of the low-E string without pushing it upward.
4. Repeat on the high E. Keep your eye level with the gap and avoid tilting the gauge.
5. Read both again. If the readings disagree, improve your positioning or lighting before recording them.
6. Write down the context. Include tuning, string set, fret, capo status and date alongside the numbers.

The diagram above shows the two measurement surfaces. It is schematic, not a printable ruler. Printing it at a different scale cannot give you a trustworthy measuring gauge.

Avoid the three most common comparison errors

Measuring from the fretboard wood includes the fret's height in your reading. Measuring to the middle or top of the string includes part of its diameter. Pressing on the string while positioning the ruler changes the gap you are trying to measure.

A capo changes the string's reference point too. If a source asks for one, use its entire procedure and associated target. Do not combine a capo measurement from one guide with an open-string target from another.

If you already have a suitable ruler and tuner, use them. The following are alternative measuring tools, not a list of three things you must buy:

Find the Cause Before Adjusting String Height

An uncomfortable guitar does not always need lower bridge saddles. First identify where the problem occurs and whether it began suddenly. That observation helps you choose the next measurement.

Symptom	Useful next check	Avoid assuming
First-position chords feel hard or go sharp	Nut clearance and fretting pressure	The entire bridge is too high
Clearance is excessive through the middle of the neck	Neck relief	Action and relief are the same measurement
One or two frets buzz	Local fret condition and clearance	Every saddle needs changing
Acoustic action rose with humid weather	Humidity and body condition	A permanent saddle reduction is needed
Acoustic action is high with little saddle showing	Overall neck, top and bridge geometry	More sanding is available
Setup changed after a new string gauge	Relief, bridge balance and tuning	The old measurements still apply

Relief and action answer different questions

Relief measures neck curvature using a held-string reference. Action measures a playing clearance using a specified fret and method. Fender's relief explanation describes using the string as a reference across the neck.

Changing excessive relief can affect action, but that does not make the truss rod a general string-height control. Once relief is appropriate, diagnose the remaining problem rather than forcing the neck straighter to reach a chart number. The truss rod guide explains the separate checks.

Test the way you actually play

Try quiet picking, your normal strum and the strongest attack you use in a song. Check bends across the frets you play, including upper positions. A setup that works for a gentle open chord may not work for a hard chorus or a wide bend.

For an electric, also listen through your normal clean amplified sound. Decide which noises actually affect the playing result. A chart cannot evaluate your fret condition, technique or tolerance for acoustic string noise, so keep the listening test alongside the ruler.

Electric and Acoustic Action Need Different Adjustments

Electric bridge adjustments

Identify your bridge before turning a screw. Individual Strat-style saddles, a three-saddle Tele bridge, a Tune-o-Matic and a locking tremolo do not share one adjustment procedure. Use a correctly fitting tool and the manufacturer's instructions for that hardware.

Record the starting position, make a small appropriate change, retune and remeasure. Check both outer strings and the intervening string arc. Moving one saddle can affect its neighbours on a shared-saddle bridge; changing tuning or gauge can also alter a floating bridge's balance.

After action and relief are stable, check fretted-note intonation. Our intonation checker helps organise that comparison using your tuner. Action height and intonation are related setup checks, but a vertical string-height difference does not specify a fore-and-aft saddle movement.

Acoustic saddle adjustments

First check humidity, relief, nut clearance and the amount of usable saddle above the bridge. A high-action acoustic with an already low saddle needs an assessment of its geometry. Taking away more material can remove adjustment room without fixing the cause.

For a conventional removable saddle, the familiar approximation is that a saddle-height change produces about half as much change at the 12th fret. That relationship does not determine whether removal is appropriate or how much saddle can safely remain. Both outer strings, break angle and any undersaddle pickup matter.

Taylor's guidance on saddle sanding treats it as a small final adjustment within a complete setup, with major changes handled through its service process. Follow the system on your guitar, including any special neck or saddle construction.

When to stop and get the guitar assessed

Stop if an adjustment resists normal tool pressure, has no useful effect, or reaches its available travel. A lifting bridge, visible crack or sudden substantial change in action also needs investigation. A ruler reading alone cannot identify the necessary repair.

Bring the measurements and the history of the change to a technician. “The low E increased from 2.5 to 3.1 mm at the same fret after moving house” is more useful than “the action feels wrong.” Include the tuning and string change history so the comparison makes sense.

Keep a Repeatable Setup Record

A short record lets you compare seasons, string sets and adjustments without guessing. It also helps you undo an unsuccessful reversible change. Record the original measurements before work, not just the final result.

Record	Example of useful detail
Instrument and hardware	Model, bridge type and any replacement neck
Strings and tuning	Set/gauges, standard tuning or your alternative
Measuring method	12th fret, open strings, no capo, playing position
Outer-string readings	Low E 2.6 mm; high E 1.8 mm
Conditions	Date and measured room or case humidity
Work and result	What changed, final readings, bends and strumming test

This example is a record format, not a report of a measured guitar or a setup recommendation. Keep your actual instrument's information in the same format each time. Photographs can help document where the gauge was placed, although a photograph's angle can also make a gap misleading.

Tuning and relief tools below support those checks. Select what you need for your instrument; a clip-on tuner works without an output jack, while the pedal tuner requires a signal connection. Owning several gauges is not a substitute for repeating the same measuring method.

The action-height calculator provides broader playing-style comparisons. The converter on this page performs a different job: it translates a reading you already have. Neither tool can inspect your frets or choose an irreversible repair from a number alone.

Guitar Action Height FAQ

What is a good guitar action height?

There is no single value for every guitar and player. Start with your manufacturer's measurement method and reference, then test normal playing and bends. The acoustic examples here are starting ranges at the 12th fret; Fender's cited Strat and Tele action tables use the 17th fret.

How do I measure acoustic guitar string height at the 12th fret in mm?

Tune the guitar, use the intended capo arrangement, and place a suitable gauge on the 12th-fret crown. Read to the string's underside without lifting it. For this article's acoustic comparison, use open strings with no capo and record both low E and high E.

Is 4/64 inch the same as 1.6 mm?

It is close, but the exact conversion is 1.5875 mm. Manufacturers often round that to 1.6 mm for practical setup work. Treat the extra decimals as conversion precision, not proof that your ruler can measure a difference that small.

How many millimetres is 5/64 inch?

Exactly 1.984375 mm, normally rounded to about 2.0 mm in a setup reference. Enter 5/64 in the fractional-inch converter to see decimal inches and millimetres together. Preserve the original unit when recording a measurement.

Should I measure a Strat at the 12th or 17th fret?

Use the fret specified by the procedure you are following. Fender's linked Stratocaster setup instructions measure action at the 17th fret. A 12th-fret reading can document your own guitar, but it should not be labelled as that 17th-fret factory check.

Is 3 mm action too high on an acoustic guitar?

Identify the string first. A low-E reading of 3 mm may work for a forceful player; that reading on the high E can feel high for many players. Check the measuring method, relief, nut and instrument condition before deciding which adjustment is appropriate.

Can the truss rod lower my action?

Correcting excessive relief can change action, but relief must be measured separately. Do not keep tightening the rod to chase a string-height target when neck curvature is already appropriate. Stop if it resists normal adjustment or has no effect.

Can I use the converter to calculate saddle removal?

No. It converts the same length between units. It does not account for saddle clearance, neck geometry, break angle or pickup fit, and it does not convert between frets. Use the acoustic diagnosis guide before considering any material removal.

Does changing string gauge mean I need to check action again?

Yes, check it after the new strings are fitted and tuned. A gauge change can affect relief and floating-bridge balance. It does not automatically require an adjustment: compare the measurements and play the guitar before deciding.

Why does a guitar buzz even when its action matches a chart?

A chart cannot account for local fret problems, neck curvature, playing attack or instrument condition. Find where the buzz occurs and whether it happens with open or fretted notes. A local problem may need a different response from raising every saddle.

For the next setup session, keep the measuring method beside the measurements. Start from a documented reference, make one appropriate change at a time, and judge the result by how the guitar plays.