The Guitar Fret Spacing Calculator gives you exact fret-slot positions for any scale length, from the nut all the way to the 24th fret. It is built for luthiers, kit assemblers, and makers cutting fretboards on a CNC, laser, or 3D printer.
How it works
Western guitars use equal temperament: every fret raises the pitch by one
semitone, a frequency ratio of 2^(1/12). Since pitch is inversely proportional
to the vibrating length, each fret shortens the string by a factor of
2^(-1/12). The distance from the nut to fret n is therefore:
d(n) = scale − scale ÷ 2^(n/12)
The traditional luthier shortcut is the rule of 18, more precisely the
constant 17.817. You divide the scale length by 17.817 to find the first
fret, then divide the remaining length by 17.817 for the next, and so on. Both
methods give the same answer because 17.817 = 1 ÷ (1 − 2^(-1/12)).
A built-in sanity check
The 12th fret is one octave up, and an octave halves the string length — so the 12th fret always lands at exactly half the scale length. If your layout puts it anywhere else, the maths is off. The calculator highlights this midpoint for reference.
Common scale lengths and their first-fret distances
Different instruments use different scale lengths, each producing a characteristic feel and tension:
| Instrument / Model | Scale length | First fret from nut |
|---|---|---|
| Fender Stratocaster / Telecaster | 25.5 in (647.7 mm) | ~1.431 in (36.4 mm) |
| Gibson Les Paul / SG | 24.75 in (628.65 mm) | ~1.390 in (35.3 mm) |
| PRS standard | 25 in (635 mm) | ~1.405 in (35.7 mm) |
| Classical guitar (typical) | 650 mm | ~36.5 mm |
| Short-scale bass (Mustang) | 30 in (762 mm) | ~1.693 in (43.0 mm) |
| Standard bass | 34 in (863.6 mm) | ~1.912 in (48.6 mm) |
These are for reference only — always enter your specific scale length for accurate slot positions.
Worked example — 25.5 in Fender scale
For a 25.5 in Stratocaster-style neck, the calculator produces positions like these:
- Fret 1: 1.431 in from nut (gap from nut = 1.431 in)
- Fret 2: 2.783 in from nut (gap = 1.352 in)
- Fret 5: 6.455 in from nut
- Fret 12: 12.750 in — exactly half the scale length ✓
- Fret 24: 21.148 in from nut, leaving 4.352 in to the saddle
The gaps shrink steadily as you move toward the body, which is why upper fret work on a long-scale bass can feel cramped compared to a shorter scale.
Practical tips for cutting slots
Cut your slots at the centreline of the calculated positions. Slot width depends on the tang thickness of your chosen fretwire — most standard wire fits a 0.023 in slot. If you are using a CNC or laser, export the list as a CSV for your toolpath software.
For multi-scale (fanned-fret) builds, run the calculator twice with the treble-side and bass-side scale lengths, then connect matching fret numbers to find each fret’s angle. Add saddle compensation at setup time rather than adjusting the fret positions themselves — the slot positions are theoretically correct as-is.