From the May/June 2020 issue of Acoustic Guitar | By Martin Keith
Scale length is an often overlooked design variable that has a considerable impact on the sound and feel of the guitar. Here’s a guide to understanding scale length on acoustic guitars.
I need your help to understand scale length. Why are there so many different variations, how is scale length measured, and how does it affect the tone of the guitar? What gauge strings are best for different scale lengths? Why should this measurement matter to me, and how should it factor in when shopping for a guitar? —Bob Lang, Starksboro, VT
Earlier in my career, I worked with Veillette Guitars, a company that specializes in unusual scales and tunings, so this topic is one I particularly enjoy. In the simplest terms, scale length refers to the length of the active/vibrating portion of the open string, between the nut and saddle. Among acoustic guitars, the most common scales are clustered around 25.4–25.5 inches and 24.75 inches. However, to determine the scale of a guitar, you can’t just measure from nut to saddle, since the bridge saddle positions are moved or compensated away from the theoretical scale point to correct intonation. The most accurate way to calculate scale is to measure the distance from the nut to the center of the 12th fret and double the result.
The basic rule of scale length is simple: For any given tuning and set of strings, longer scales have higher tension. Once again, it’s important to note that this only applies to the area of string that is vibrating between the nut and saddle. The string beyond those points (called the afterlength in violin-family instruments) can affect aspects of how the string feels, as a greater afterlength offers more stretch than a short one, but does not impact the tension of the string at its target pitch.
When doing a setup, scale length is an important consideration. Instruments with shorter scales can be more demanding for a number of reasons: The lower tension means fret buzzes can be caused more easily, and the intonation is often trickier to dial in accurately. A player accustomed to low action on a 25.5-inch fretboard may be comfortable with slightly higher action on a 24.625-inch instrument, whereas someone who usually plays short scales may want to choose a lighter string gauge if they buy a longer-scale guitar.
It’s not uncommon for players to wonder how much difference a change of 3/4 of an inch or less really makes. Let’s consider the overall tension of a typical light (.012–.053) string set. On a 25.5-inch scale fretboard, the combined tension at standard tuning is 160.5 lbs., whereas at 24.75 inches the tension is 151.24. Therefore, a three-percent change in scale length can result in a six-percent change in tension. By comparison, a set of .011–.052 strings adds up to 148.6 pounds. The result is that the tension of .012s on the shorter scale will be very comparable to the .011s on the longer scale.
Alongside string tension, you must also consider string flexibility. Thicker strings are less flexible, as are shorter lengths of string. As a string loses its flexibility, it starts to exhibit less accurate intonation, which is once again why the thick low strings require greater compensation than the thin high strings. Excessively stiff strings also tend to sound less musical, with odd harmonics and overtones that don’t relate to the notes being played.
Low bass notes, therefore, are better reproduced with long strings than with short ones, as the length allows a thinner, more flexible string to be used. Treble strings, on the other hand, can sound thin, harsh, and unpleasant if the tension is too high, and many players favor the warm, thick tone of the trebles on shorter scales. Therefore, the builder and player must find the happy medium between clean, well-behaved bass strings and pleasant, musical trebles by choosing the best combination of scale and string gauges. The ideal example of this is the grand piano, which uses a much longer scale length for the low bass strings than the treble strings. Imagine how different the strings would need to be in order to make that range work with a single scale length!
Although the guitar has considerably less range than the piano, there are still cases where a shorter scale is not ideally suited for the player’s needs—these might include extended tunings with low D or C notes, or guitars with more than six strings. In an attempt to improve bass-string response without compromising the quality of the high notes, some modern makers offer multiscale or fan-fretted instruments, which have longer bass string scales and shorter trebles. Such instruments have frets that are not parallel, which can be a bit intimidating at first glance, but this design is gaining popularity with players who appreciate the more even tension and response it can offer with extended-range tunings. California luthier Ralph Novak is widely credited with proving and popularizing this innovative approach in the custom guitar world, and larger manufacturers are now following suit with production multiscale instruments.
Paying attention to scale length when shopping for a guitar can be very helpful. Some guitars will just feel right, and the scale is often a big part of that. The fret-to-fret variation between different scales is fairly small—for example, between the two scales discussed above, the difference in distance between the first and second frets is only 40 thousandths of an inch. But even these small differences can be felt and appreciated by most players. For a guitarist who has always played Gibsons, for example, the longer scale of a Martin dreadnought or OM may well take some adjustment. Keeping this in mind when evaluating and comparing guitars allows the player to make more accurate judgments about which aspects of the guitar are impacting the playing experience—action can be lowered, but scale length is fixed, and if a guitar feels uncomfortable, it is useful and important to understand why.
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Guitar designers often adjust scale length to optimize an instrument for a particular purpose—for example, jazz archtops with pickups often have shorter scales, which yield thicker, warmer sounding trebles and warm basses with a smooth attack. By contrast, a builder aiming for the bluegrass flatpicker market will likely use a longer scale to get the added punch and volume that the higher string tension can produce. When building a long-scale guitar, the builder must also anticipate the higher tension and brace accordingly, or the instrument may not survive in the long term. This is one reason many fingerstyle players have gravitated towards 00- and 000-style guitars, as their shorter scale (24.9 inches) permits lighter bracing, which yields a more sensitive and dynamic instrument.
At the extreme end of the scale spectrum are baritone guitars (see “Taking on the Tweener” in the March/April 2020 issue), which usually range from 27–30 inches in scale and are designed to be tuned down as far as a fifth below a standard guitar. The heavier string gauges, combined with the long scale, can make the low notes on these guitars quite impressive—and help to illustrate the combined effect of gauge and scale on the quality and character of the guitar’s tone. Capoing a baritone back up to E will result in the same tuning as a standard guitar, but with a very different timbre and tone.
Scale length is one of the fundamental building blocks of a guitar’s recipe, with a wide-ranging impact on the feel, tone, and performance. Understanding how it interacts with your setup, string choice, and playing style will make it much easier to properly adjust your guitar, and may help guide you towards an instrument that feels just right.
Martin Keith is a luthier, repair and restoration expert, and working musician based in Woodstock, New York. martinkeithguitars.com.
This article originally appeared in the May/June 2020 issue of Acoustic Guitar magazine.