The actual length of the scale is the measured length between the backside of the nut (or from the center of the zero fret, (if there is one installed) to the center of the saddle midway between the 3rd and 4th strings.
The scale length of the guitar is one subject that can be very controversial. Some players like a longer scale length, while others prefer a shorter one. Reasons for this can vary from slightly less tension on the strings, to shorter distance between frets. You will find that shorter scales give warmer tones with less tension on the strings and therefore can give an easier playing guitar.
The classical guitar on the other hand, is much more influenced by the scale length. You will find that the grand concert classical guitars are all grouped between 650 and 660 mm length, which will generate greater volume because a greater string tension is required to bring them up to standard tuning.
Antonio De Torres established the scale length used on the classical guitar at 650 mm or 25.6 inches, and you will see many guitars built to that standard. Today though, many concert classical guitars are built to the more standardized 660 mm or 26 inches. The classical guitar plans that we have available at Georgia Luthier Supply often offer a choice of either 650mm or 660mm.
How Fret Spacings Are Derived:
A musical string may be divided by the twelfth root of two 12√2, or approximately 1.059, and the quotient taken as the location of the next semitone pitch from the bridge of the instrument. This quotient is then divided again by 1.059 to locate the next semitone higher, and so on.
Alternatively, the string may be divided by 12√2/12√2-1, or approximately 17.817, and the quotient taken as the location of the next semitone pitch from the nut of the instrument. The remainder is again divided by 17.817 to locate the next semitone pitch higher, and so on.
For centuries the divisor 18 was used instead; this “Eighteen Rule” produced a sort of rough compensation. Actual fret spacing on the fretboard was often done by trial and error method (testing) over the ages. However, since the nineteenth century the availability of precision measuring instruments has allowed frets to be laid out with mathematical accuracy.
What We Use Today:
With the advent of computers, the Internet and several free programs, you can easily compute your own customized fret spacings and have absolute accuracy with anything you choose. Also, by simply using the above formulas, you can choose your scale length, divide by the chosen formula, subtract the quotient, and continue until you reach your target fret number.
A Word Of Caution:
If you use a printed version of the fret scale, because of the accuracy required for fret spacings, you should be aware that as humidity and temperature change, so does the paper it is printed upon. There can be a difference of a couple of percent from high to low humidity, which can seem insignificant, but it will make quite a difference in determining the absolutely perfect scale length and fret spacing. Therefore, never layout your fret spacings from a printed graphical fret spacing diagram. Always layout the frets by actually measuring them or by using a mechanical fret miter saw or perhaps use one of our Fret Slotting Templates.
All of our guitar plans have printed fret spacings listed in a table. To ensure accuracy, each measurement to each consecutive fret is measure from the backside of the nut. This eliminates a cumulative error of measuring from fret to fret. Also when you mark your frets do so with either a scratch awl, or a cutting edge to give you a very precise line.
Free Guitar Scale Calculator:
Stewart MacDonald provides a free Guitar Scale Calculator. Just input your desired scale, the number of desired frets and press the button and you will have it in both fractional inches and millimeters. You can then copy and print this and make your very own Guitar Scale Template.