About the Fret Position Calculator
This fret position calculator gives the distance from the nut to each fret for any scale length, using the equal-temperament formula that every modern guitar, bass, mandolin and ukulele is built on. It also lists the spacing between neighbouring frets and the remaining distance from each fret to the saddle, ready to transfer to a fretboard blank or a slotting template.
It is meant for luthiers building or refretting an instrument, students checking a kit, and players curious why frets get closer together up the neck. Enter the scale length in inches or millimetres — all results come back in the same unit — and choose how many frets you need.
Positions are theoretical and measured from the front edge of the nut along the centre line of the neck. Real builds add a small compensation at the saddle (and sometimes the nut) to correct intonation for string stiffness and action height; this tool does not add compensation.
With the default inputs, the nut to selected fret is 12.75. Change any value above to recalculate instantly.
How to use the fret position calculator
- 1Enter the scale length of the instrument and choose inches or millimetres.
- 2Set how many frets the fretboard has.
- 3Pick a fret to see its exact position, spacing and distance to the saddle.
- 4Use the table to mark every slot, measuring from the nut each time to avoid cumulative error.
Formula and method
In 12-tone equal temperament each fret raises the pitch by one semitone, a frequency ratio of 2^(1/12). Because a string's pitch is inversely proportional to its vibrating length, the length left after fret n is L ÷ 2^(n/12), so the distance from the nut is L minus that. The 12th fret is therefore at exactly L/2 and the 24th at 3L/4.
The traditional "17.817 rule" (divide the remaining length by 17.817 to get the next fret) gives the same result, because 1 ÷ (1 − 2^(−1/12)) = 17.817. The older "rule of 18" divides by 18 instead, which places frets slightly too close to the nut and makes fretted notes play progressively flat further up the neck; it is included for historical comparison only.
- dₙ
- Distance from the nut to fret n
- L
- Scale length (nut to saddle)
- n
- Fret number
Worked examples
Fender-style 25.5" scale, 12th fret
The 12th fret is exactly half of 25.5 in, i.e. 12.75 in from the nut. The 1st fret is 25.5 × (1 − 2^(−1/12)) = 1.4312 in, and the 22nd fret lands at 18.3443 in. The gap between the 11th and 12th frets is 0.7582 in.
Classical guitar, 650 mm, 19 frets, 5th fret
On a 650 mm classical scale the 5th fret is 650 × (1 − 2^(−5/12)) = 163.05 mm from the nut, leaving 486.95 mm to the saddle. The 19th fret sits at 433.09 mm.
34" bass, 24th fret
Two octaves up, the 24th fret is at three-quarters of the scale: 34 × 0.75 = 25.5 in, with 8.5 in left to the saddle. Frets up there are only about half an inch apart.
Frequently asked questions
How do you calculate fret spacing?+
Distance from nut to fret n = scale length × (1 − 2^(−n/12)). Equivalently, divide the remaining string length by 17.817 to find the next fret. Always measure each fret from the nut rather than from the previous fret to avoid accumulating errors.
Where is the 12th fret?+
Exactly halfway between the nut and the saddle in equal temperament. On a 25.5 in scale it is at 12.75 in; on a 24.75 in scale at 12.375 in; on a 650 mm classical guitar at 325 mm.
What is the difference between the rule of 18 and 17.817?+
The rule of 18 is an old approximation that divides the remaining length by 18. It places frets slightly too close to the nut, so the 12th fret ends up short of the true octave. 17.817 is the exact equal-temperament constant.
How do I measure scale length?+
Measure from the front edge of the nut to the centre of the 12th fret and double it. Bridge saddles are set slightly behind the theoretical scale length to compensate intonation, so measuring nut-to-saddle usually reads a little long.
Does this work for fanned-fret or multiscale necks?+
Yes, run it twice: once with the bass-side scale length and once with the treble-side length. Each fret runs in a straight line between the two calculated positions, with the perpendicular fret chosen where the two sides align.