The term “scale length” tends to get thrown around a lot by cigar box guitar builders, but there is also a lot of confusion amongst newer builders about what this term means. Fortunately, the concept is pretty straightforward: the scale length of an instrument is the distance from the nut to the bridge. Scale lengths vary depending on overall size of the instrument: mandolins have a short scale length around 14″, guitars vary but on average are around 25.5″, and larger instruments like basses have even longer scale lengths.
Scale length affects a number of things, but most importantly it affects where fret locations will be – in other words, where different notes will be found on the strings. Even if your instrument is not fretted, your scale length affects where you will place the slide to find the key chords. Scale length is even more important if you are fretting your instrument — you have to be certain of your scale length before you start marking and cutting fret slots, or your instrument will never intonate correctly.
For much more information on fretting and scale lengths, check out C. B. Gitty’s Fretting Guide, a very affordable introductory guide to fretting, with a focus on using standard tools and do-it-yourself methods. The guide is available both as an immediate eBook download version and as a PDF eBook on a shipped CD.