Measure a guitar’s scale length by measuring the distance from the inside edge of the nut (adjacent to the fretboard) to the middle of the 12th fret. This number is then doubled as it represents half the distance from the inside of the nut to the saddle.
Today we are going to cover how to measure guitar scale length, including:
1. The correct way to measure scale length
2. Why the length of your strings between the nut and the saddle is not an accurate way to measure scale length
3. How guitars are designed to compensate for the various elements that affect scale length
Why scale length is measured between the nut and 12th fret.
Many people believe the true scale length of a guitar is the length of the guitar strings that can freely vibrate, this is even how Wikipedia defines scale length but this is not entirely correct.
If the properties of each string were the same this would indeed be the case, but as can be seen, when observing your high E string in comparison to the thicker, wound low E, this isn’t the case at all.
Guitar strings are suspended between the saddle (the last point of contact for the strings on the guitar body) and the nut (the last point of contact on the neck) adjacent to the first fret of the guitar. When a guitar is played, the entire length of the string vibrates between these two points of contact.
Common sense would dictate that scale length could then be measured by measuring the distance between the nut and the saddle, rather than measuring to the 12th fret and then doubling the number.
However, this is not an accurate way to measure scale length because the saddle is often seated within the bridge of the guitar at an angle. Due to the angle of the bridge, each string will be a slightly different length.
Why is the Bridge Saddle Seated on an angle?
I hate to break it to you but your guitar is probably never 100% completely in tune. Don’t despair, all guitars suffer from this flaw to some degree.
Intonation (accuracy of pitch) is affected by several factors, but two of the biggest factors are the strings ability to vibrate and its ability to stretch, both of which are affected by the string’s mass.
When notes are fretted on a guitar neck, the guitar string is pushed down against the fretboard, causing it to stretch.
We know that when the string’s length is shortened e.g. by fretting a note and reducing the length that can vibrate, the pitch is raised. But it is also the case that when the string is pressed against the fretboard the string stretches, unlike when playing an open string.
To complicate matters the amount of stretch is affected by the length of the string, which as we know changes when we fret notes.
To further complicate matters, as each string is of a different thickness (gauge) the amount of stretch will vary based on the properties of each string, even considering the changing length of the string when fretted. It is also true that the mass of each string also affects the strings ability to vibrate.
As you may expect, the string’s ability to vibrate and stretch affects the pitch of the string, and as guitar strings come in different thicknesses (gauges) each string has to be compensated for individually.
In a nutshell, this means the actual vibrating length of each string must be adjusted based on the physical properties of the string. To compensate for these factors, your bridge saddle is positioned on an angle, which increases the length of the heavier, wound bass strings compared to the higher strings e.g. the E and B strings. The additional length the angle affords the lower heavier strings compensates for the additional mass of the strings.
However taking into account all the different factors listed above it is not an exact science, meaning your guitar is likely never 100% in tune.
On electric guitars, (at least in many cases) each string has an adjustable metal saddle. When adjusted (by turning a spring-loaded screw at the rear of the saddle) the saddle moves closer to the nut or further away, ultimately changing the length of the string fractionally. Additional smaller screws can also be adjusted to raise the height of each individual saddle to compensate for the different thicknesses of each string.
The image to the left shows a typical Fender bridge. Tune-O-Matic bridges, as seen on many Gibson electric guitars look and work slightly differently, although the basic principles are the same.
While this method has been used on a small number of acoustic guitars over the years, this isn’t the case for most acoustic guitars as adding metal in any form to the bridge of an acoustic guitar will affect the soundboard’s ability to resonate, which indirectly affects both tone and volume.
Hence, all good acoustic guitars feature an angled saddle which compensates for the properties of the guitar strings and differences in gauges.
When it comes to classical guitars, the bridge will be either completely straight or be seated at a slight angle.
This is because the difference in mass between the nylon high E and low E for instance, on a classical guitar, is not comparable to the differences in mass of electric guitar strings.
Compensated saddles also fractionally change the length of a guitar string. A compensated saddle is a saddle that has wedges removed so the point of contact for the string is adjusted, resulting in a fractional change to string length between the nut and saddle.
Compensated saddles are used to adjust for the differences between the high E and B strings mass. As the B and E strings are unwound, unlike the heavier bass strings the different thicknesses of these two strings have a larger bearing on the tension of the strings and are further adjusted by using a compensated saddle along with the angle of the saddle affecting overall string length.
While scale length itself is simple to measure (from inside of the nut to the 12th fret) as can be seen through the use of angled and compensated saddles, not to mention other innovations such as multi-scale or fanned frets the scale length issue has long been a problem for stringed instruments and makes simply measuring the length of the string able to freely vibrate inaccurate.
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