650mm vs 664mm Mensur: Try Both on Classical and Flamenco Guitars

For most classical and flamenco players, a 650mm mensur is the practical default. It fits typical hand spans and repertoire without extra reach, and most modern classical guitars are built this way. Choose a 664mm scale only if you have notably large hands or specifically want the tighter bass and extra projection historically associated with Ramirez-style concert instruments.

TL;DR:

An identical standard string set produces about 41.0 kilograms of tension at 650mm and 43.8 kilograms at 664mm, roughly a 7% increase.

The spacing difference is most noticeable in the first four or five frets, so test first position barre chords and wide stretches before choosing.

A 664mm scale can give the bass a tighter feel in large halls, but soundboard design and bracing influence projection more than mensur.

Tuning down a half step cuts tension by about 5.6%, while lighter strings or nylon trebles can soften a demanding 664mm instrument.

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Scale Length Basics: What 650mm and 664mm Actually Mean
String Tension: Comparing 650mm and 664mm Under Load
Playability and Ergonomics: What Changes Under the Left Hand
Tone and Projection: What Mensur Really Changes
How to Choose Between 650mm and 664mm
How We Help You Test and Compare Mensur in Person
A Pragmatic Take on Scale Length Tradition
Try Before You Buy: Services That Take the Guesswork Out of Mensur
FAQ
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Scale Length Basics: What 650mm and 664mm Actually Mean

Scale length, or mensur, is measured from the nut to the center of the 12th fret, then doubled to get the full vibrating string length. A guitar labeled 650mm has a theoretical vibrating length of 650 millimeters between nut and saddle, while a 664mm instrument stretches that distance by 14 millimeters.

That nominal number is not quite the real one. Builders add saddle compensation, moving the saddle slightly back from the mathematical midpoint, because a vibrating string under tension needs a touch of extra length to stay in tune as you fret it. Some luthiers also compensate the nut slightly forward. The result is that the true vibrating length and the “650” or “664” printed in a spec sheet differ by a small but real margin, a detail confirmed in technical breakdowns of scale length definitions and compensation.

The small difference in scale length between 650 and 664 millimeters does not distribute evenly across the fretboard. Frets near the nut, where your hand does most of its stretching work, show a larger absolute gap than frets up near the body. That is why the difference feels more significant in first-position chords than in upper-register melodic lines.

A few practical points worth keeping in mind as you compare instruments:

The 650mm scale is the modern standard for mass-produced and most contemporary handmade classical guitars.
The 664 to 665mm range traces back to the Ramirez workshop tradition and remains common on some concert-oriented builds.
Saddle and sometimes nut compensation mean no two guitars with the “same” mensur are perfectly identical in vibrating length.
Fret spacing differences are largest in the first five frets, where hand position matters most for chord shapes.

If you want a deeper walkthrough of how builders define and measure this dimension, our guide on what mensur means on a guitar covers the measurement process in more detail.

String Tension: Comparing 650mm and 664mm Under Load

Longer strings under the same tuning and gauge carry more tension, and the numbers back that up clearly. A standard classical string set strung on a 650mm instrument produces roughly 41.0 kilograms of total tension, while the identical set on a 664mm scale rises to about 43.8 kilograms, according to the classical guitar string tension calculator.

Scale length	Approximate total tension (standard set)	Tension classification
650mm	~41.0 kg	Standard
664mm	~43.8 kg	Long scale

The physics behind this is straightforward: tension rises with the square of the vibrating length for a given pitch and string mass, so a modest increase in scale length produces a proportionally larger jump in tension. Tuning down relaxes that tension. Each half-step drop reduces tension by roughly 5.6%, which means a 664mm guitar tuned down a half step lands close to a standard-tuned 650mm instrument in overall feel, per the same tension calculator data.

String material matters just as much as scale length. Fluorocarbon trebles typically run at somewhat higher tension than nylon of a comparable gauge, so a player on a 650mm guitar who wants more resistance under the fingers can switch material rather than hunt for a longer-scale instrument. The reverse works too: a 664mm player who finds the feel too stiff can drop to a lighter tension set or swap to nylon trebles to narrow the gap. For a closer look at how gauge and material choices interact with scale length, see our piece on choosing string tension for vintage classical guitars.

Pro Tip: If you love the tone of a 664mm guitar but find the tension demanding, try a light-tension set before assuming the scale length itself is the problem.

For flamenco repertoire, where speed and low action matter more than raw tension, many players favor lighter gauges regardless of mensur, which keeps the right-hand attack fast on either scale.

Playability and Ergonomics: What Changes Under the Left Hand

The added length on a 664mm guitar stretches fret spacing across the whole neck, but the effect is most noticeable in the first four frets, where common chord shapes and position changes live. A stretch that feels comfortable on a 650mm neck can feel noticeably tighter on a 664mm neck, particularly for barre chords that span four or five frets in first position.

Nut width and string spacing are often linked to scale length in classical guitar design, since a longer scale typically pairs with marginally wider spacing to keep right-hand accuracy consistent. But neck profile and fretboard radius influence comfort just as much as mensur, so two 664mm guitars from different builders can feel quite different in the hand. Forum discussions among players comparing 65 and 66 class scales note that the real-world millimeter difference at the first few frets, often 14mm or less, is small in isolation but can accumulate across a demanding passage, according to one long-running player discussion.

A few ways to test this before committing to one scale or the other:

Play a full barre chord in first position and note whether your fourth finger reaches comfortably.
Run a stretched scale passage, like a two-octave arpeggio, and compare fatigue between the two scales.
Check your thumb position behind the neck during a left-hand stretch rather than just the fingers.
Ask about adjusting string gauge or action if a mensur feels promising tonally but tight physically.

Setup adjustments can soften a scale length that otherwise suits your ear. Lower action, a slightly flatter fretboard radius, or a lighter string gauge all reduce the physical demand of reaching across a longer neck. Our explainer on how the neck affects sound, tension, and playability walks through these setup variables in more depth.

Tone and Projection: What Mensur Really Changes

A longer scale does not automatically mean a louder guitar; for curated examples of acoustic music contexts and tonal variety, you can explore acoustic programming that highlights diverse styles and instrument nuances. Soundboard design, bracing pattern, and overall build quality drive projection far more than the 14mm difference between 650 and 664, a point borne out by acoustic analysis of guitar soundboard behavior, which shows that a well-built 650mm instrument can match or exceed the carrying power of a longer-scale guitar with a less responsive top.

A well-braced 650mm soundboard can project as effectively as a longer-scale guitar, according to acoustic analysis of soundboard design, which makes top quality and bracing the more reliable predictor of volume than mensur alone.

That said, scale length does shape tone in subtler ways. A longer mensur under equivalent tuning carries more string tension, which tends to produce a tighter, more focused bass response and can give a slight edge in carrying power in a large hall. A shorter 650mm scale, carrying less tension for the same pitch, often feels more pliable under the right hand and produces a mellower, more expressive response that many flamenco and fingerstyle players favor.

Some considerations when weighing tone against mensur:

A concert player filling a large hall may lean toward 664mm for its tighter low end and slightly stronger projection under equal construction quality.
A flamenco player prioritizing speed and expressive dynamics often prefers the lighter feel of a 650mm neck.
Setup changes, like a higher-tension string set or adjusted saddle height, can push a 650mm guitar’s projection closer to a long-scale instrument without changing the neck.
No scale length substitutes for a well-built top; a mediocre soundboard will underperform at either length.

If projection is your main concern, our guide to improving the acoustic quality of a classical guitar covers setup changes that often matter more than scale length alone.

How to Choose Between 650mm and 664mm

Deciding between the two scales comes down to a short list of practical questions rather than brand loyalty or tradition for its own sake.

Measure your hand span by checking how comfortably you reach a four-fret barre chord in first position on a 650mm guitar.
Consider your repertoire. Fast flamenco falsetas and fingerstyle passages often favor the lighter feel of 650mm, while dense classical works with wide left-hand stretches can suit either scale depending on your reach.
Think about your venue. If you regularly play unamplified in large rooms, the tighter bass of a 664mm instrument may offer a small edge.
Account for any hand or wrist strain. Players managing tendon issues or limited flexibility generally do better on the shorter scale.
Test identical passages on both scales using, where possible, the same string gauge and tension, so you are comparing the neck rather than the strings.
Check open-string feel first, then fretted stretches, since open strings reveal raw tension while fretted notes reveal ergonomic fit.
Have the nut spacing and action measured on any guitar you are seriously considering, since these affect comfort independently of mensur.

Pro Tip: Bring your own well-worn piece, not a warm-up exercise, when comparing scales in person. Familiar repertoire reveals tension and stretch issues that scales and arpeggios can mask.

If a guitar feels right tonally but slightly demanding physically, a setup adjustment, lighter strings, or a small action change, often resolves the issue before you rule out the instrument. For a longer walkthrough of this decision process, see our guide on choosing the right scale length for a classical guitar.

How We Help You Test and Compare Mensur in Person

Reading tension charts only goes so far. We offer playing appointments where you can try multiple instruments side by side, including models with different scale lengths, to compare their feel under similar conditions.

During a trial, we discuss setup factors like action height, nut spacing, and string tension on each instrument to help you understand their playability. If a guitar feels close but not ideal, setup adjustments such as altering action, refretting, or restringing can help improve comfort and playability. If you are weighing a historic long-scale instrument against a modern 650mm build, bring a few minutes of your own repertoire rather than relying on store demo pieces, since familiar material shows stretch and tension issues fastest.

A Pragmatic Take on Scale Length Tradition

The 664 to 665mm tradition tied to Ramirez-era concert guitars carries real weight in classical guitar history, and some players still prefer it for its tighter bass and historic lineage. But the 650mm standard became dominant for good reason: it fits a wider range of hands and repertoire without asking players to adapt their technique to the instrument.

My honest read is that most players overvalue mensur tradition and undervalue comfort. A guitar you can play relaxed for two hours will usually sound better than a historically “correct” instrument that fights your hand. Choose based on reach, repertoire, and venue, not on which scale a famous workshop favored a century ago.

— Vintage

Try Before You Buy: Services That Take the Guesswork Out of Mensur

Choosing between 650mm and 664mm is easier when you can play real instruments side by side rather than compare spec sheets. Playing appointments are available to let you test classical and flamenco guitars in person before committing.

A few ways we support that decision:

Exclusive playing appointments where you compare multiple instruments and scale lengths under the same conditions.
A curated selection of vintage guitars and classical guitars (nylon) spanning both scale traditions.
Certification and valuation services so you know exactly what you are buying when an instrument has historic or collectible value.
Restoration and setup work that can adjust action, frets, or stringing to fine-tune how a given mensur feels in your hands.

If you are ready to compare instruments hands-on, book an exclusive playing appointment or browse our concert guitar category to see what is currently available.

FAQ

What is the difference between 650mm and 664mm mensur?

The difference is 14 millimeters of vibrating string length, which raises string tension by roughly 7% on a 664mm scale compared to 650mm using an identical standard string set. That extra tension translates into a tighter feel under the fingers and slightly wider fret spacing, most noticeable in first-position chords.

Does a longer mensur make a guitar louder?

Not necessarily. Soundboard design and bracing have a bigger effect on projection than scale length, and a well-built 650mm guitar can match the carrying power of a longer-scale instrument with a less responsive top. A 664mm scale does tend to produce a tighter bass response, which some players perceive as more projecting in a large hall.

Which mensur is better for small hands?

Players with smaller hands generally find 650mm easier to manage, since the shorter fret spacing reduces the stretch needed for barre chords and wide intervals, as noted in technical breakdowns of scale length and hand fit. If a 664mm guitar still appeals tonally, a lighter string gauge or adjusted action can ease the physical demand.

Can I change string tension without changing mensur?

Yes. Switching string material, fluorocarbon trebles run about 5% higher tension than nylon, or tuning down a half step, which cuts tension by roughly 5.6% per step, lets you adjust feel on a fixed scale length using the same tension scaling principles. This is often the fastest way to close the gap between how a 650mm and 664mm guitar feel.

Should flamenco players use a different mensur than classical players?

Most flamenco players favor the standard 650mm scale for its lighter feel and faster response under rapid right-hand technique. Some classical players choose 664mm for its historic association with concert-style projection, but the choice ultimately depends on hand size, repertoire, and venue rather than genre alone.