MasterTool

Fret Calculator

Calculate fret from the published formulas and tables for the craft.

Loading calculator…

What this tool does

Calculate fret from the published formulas and tables for the craft. Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.

How to use the Fret Calculator

  1. Enter or select scale length (inches).
  2. Enter or select fret number.
  3. Read the calculated result; change any measurement to compare alternatives.

Formula

distance from nut = scale length × (1 − 2^(−fret ÷ 12)); remaining string length = scale length × 2^(−fret ÷ 12)
scale
Scale length (inches)
fret
Fret number

Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.

Worked example

For fret calculator, the following measurements illustrate the exact method: Scale length (inches): 25.5; Fret number: 12.

Inputs

  • Scale length (inches)25.5
  • Fret number12

Result

  • Distance from nut (inches)12.75
  • Distance from nut (mm)323.85
  • Distance from previous fret (inches)0.76
  • Remaining string length nut-side to bridge from fret (inches)12.75

Results explained

Distance from nut (inches)
Distance from nut (inches) from the formula above. Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.
Distance from nut (mm)
Distance from nut (mm) from the formula above. Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.
Distance from previous fret (inches)
Distance from previous fret (inches) from the formula above. Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.
Remaining string length nut-side to bridge from fret (inches)
Remaining string length nut-side to bridge from fret (inches) from the formula above. Exact equal-temperament formula (the modern form of the rule of 18). Fret 12 always lands exactly halfway — 12.75 in on a 25.5 in scale — because it must halve the string to raise the pitch an octave.

Frequently asked questions

Distance from the nut for fret n = scale length × (1 − 2^(−n/12)). On a 25.5 in Fender-style scale, fret 1 sits about 1.431 in from the nut and fret 12 sits at exactly 12.75 in — half the scale.

The historical luthier rule divides the scale by 17.817 (often rounded to 18), places a fret, then repeats on the remaining length. It approximates the exact 2^(n/12) formula used here; cumulative rounding in the old rule drifts slightly sharp, which modern builders avoid by using the exact formula.

Halving a vibrating string doubles its frequency — an octave. Equal temperament puts the octave at semitone 12, and 2^(−12/12) = 0.5, so the distance formula returns exactly half the scale length for fret 12 on any instrument.

Spacing scales proportionally. A 24.75 in Gibson-style scale compresses every fret position by about 3% versus 25.5 in, which is part of why shorter scales feel slinkier; the ratios between frets stay identical.

Run this calculator once per scale length. For fanned-fret (multi-scale) instruments, calculate each string's fret line with that string's own scale (for example 25.5 in on the treble side, 27 in on the bass side) and connect the points.