Fret Calculator
Fret positions from the nut and the spacing between frets for any scale length in equal temperament (12-TET), for guitars, basses, ukuleles and other fretted instruments, in mm or inches.
Result…
How it's calculated
Distance from the nut to fret n: d = L − L ÷ 2^(n ÷ 12) Gap between frets n − 1 and n: d(n) − d(n − 1) Fret 12 sits at L ÷ 2
In twelve-tone equal temperament each fret raises the pitch by one semitone, a frequency ratio of 2^(1/12). Frequency is inversely proportional to the vibrating length, so the string left after fret n is L ÷ 2^(n/12) and the fret sits L − L ÷ 2^(n/12) from the nut. The 12th fret is exactly halfway, one octave up, and the frets get closer together further up the neck. The older "rule of 18" (17.817) gives the same result; the preset scale lengths are labelled examples, not standards. 1 in = 25.4 mm exactly.
Your numbers, step by step
About the Fret calculator
This fret calculator gives the distance from the nut to every fret, and the gap between neighbouring frets, for any scale length in twelve-tone equal temperament. It uses d = L − L ÷ 2^(n ÷ 12), so each fret shortens the vibrating string by one semitone. Choose one of the labelled example scale lengths, such as 25.5 in, 24.75 in, 34 in for a bass or 17 in for a tenor ukulele, or enter your own, and work in millimetres or inches. Pick from 1 to 24 frets. The steps list every fret position in both units, and the chart shows how the spacing shrinks up the neck. It is useful for building or refretting a guitar, bass, ukulele, mandolin or cigar box guitar, checking a slotting template, or seeing why the 12th fret sits halfway along the string.
How to use it
- Choose a “Scale length” example, or pick your own and type the length.
- Pick the “Units”: mm or inches.
- Enter the “Number of frets”, from 1 to 24.
- Read each fret's distance from the nut in the steps, and the gaps in the chart.
Worked example
For a 25.5 in (647.7 mm) scale, the first fret sits 647.7 − 647.7 ÷ 2^(1/12) ≈ 36.35 mm from the nut. The 12th fret is at exactly half the scale, 323.85 mm. The 22nd fret is about 465.95 mm from the nut, only 10.81 mm past the 21st, leaving about 181.75 mm to the saddle.
Updated
Questions people ask
How do I calculate fret positions for a guitar?
For fret n, subtract L ÷ 2^(n ÷ 12) from the scale length L. Measure every fret from the nut rather than adding up gaps, so small errors don't build up.
What is the rule of 18 for fret spacing?
It is an older method that divides the remaining string length by about 17.817 for each fret, which is the same as multiplying by 2^(−1/12). The original rule of exactly 18 puts frets slightly flat, which is why builders moved to 17.817.
How do I measure my scale length?
Measure from the front edge of the nut to the centre of the 12th fret and double it. Measuring to the saddle includes compensation, which makes the result a little longer than the true scale length.
Why are frets closer together higher up the neck?
Each semitone shortens the string by the same ratio, not the same distance. As the string gets shorter, the same ratio is a smaller step. To see the pitch each fret plays, use the note frequency calculator.
Does the fret calculator include saddle compensation?
No. It gives ideal equal-temperament positions for the nominal scale length. Compensation depends on string gauge, action and tuning, so set the saddle by ear or with a tuner after the frets are in.