Guitar Fret Position Calculator
Fret placement on a guitar, bass, or any fretted instrument follows directly from equal temperament: each fret shortens the vibrating string so the next note is a precise semitone higher. The distance from the nut to a fret is the scale length minus the scale length divided by two raised to the fret-over-twelve power. This calculator takes your scale length and a fret number and returns the distance from the nut, the distance from the previous fret, and the remaining length to the bridge. Luthiers and builders use it to lay out a fingerboard accurately; the twelfth fret always lands at the exact midpoint.
Fret position formula
Distance from nut = scale - scale / 2^(fret / 12)
Remaining to bridge = scale - distance from nut = scale / 2^(fret / 12)
Distance from previous fret = position(fret) - position(fret - 1)
Fraction of scale = distance from nut / scale
The output unit matches the scale-length unit you enter, inches or millimetres. The twelfth fret sits at exactly half the scale length, the octave point.
Fretboard layout context
- Common scale lengths: Fender-style 25.5 in, Gibson-style 24.75 in, classical 650 mm, bass 34 in.
- The twelfth fret is always at the midpoint; use it to verify your scale length.
- Each fret is closer to the next as you move up the neck, a fixed ratio of the remaining length.
- Measure scale length from the nut to the centre of the bridge saddle.
- Set intonation at the saddle, not by moving frets; these are the geometric positions.
Fret position: frequently asked questions
How is fret position calculated?
The distance from the nut to a fret equals the scale length minus the scale length divided by two raised to the fret number over twelve. This places each fret so that the string sounds an equal-tempered semitone higher than the open string. The twelfth fret sits exactly halfway along the scale, sounding an octave.
What is the rule of 18 or 17.817?
A historical shortcut places each fret 1/17.817 of the remaining string length from the previous fret. The constant 17.817 is 1 divided by (1 minus the twelfth root of one half). The exact equal-temperament formula used here is more precise, but the constant explains why luthiers once spoke of the rule of 18.
What is a common guitar scale length?
Fender-style electric guitars typically use a 25.5 inch scale, Gibson-style guitars about 24.75 inches, and classical guitars around 25.6 inches (650 mm). Basses are longer, commonly 34 inches. Enter your instrument's scale length, the distance from the nut to the centre of the bridge saddle, for accurate fret spacing.
Why is the twelfth fret at the halfway point?
Twelve semitones make an octave, and an octave doubles the frequency, which means halving the vibrating string length. So the twelfth fret must sit at exactly half the scale length. This is a useful check: if your twelfth fret is not at the midpoint, the scale length entered is wrong.
Does fret position account for intonation compensation?
No. This gives the theoretical fret positions for an ideal string. Real strings need a small bridge compensation because pressing a string sharpens its pitch. Builders set intonation at the saddle, not by moving frets, so these positions remain the correct geometric layout.
Official sources
- UNSW School of Physics: Strings, standing waves and harmonics.
- UNSW School of Physics: Note names, MIDI numbers and frequencies.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.