Fret Distance Calculator

Every fret on a guitar sits at a precise, mathematically fixed point. The twelfth root of two governs it all: each semitone shortens the vibrating string by the same ratio, which is why the 12th fret lands exactly halfway between the nut and the bridge. Get the math right and every note plays in tune; get it wrong and the instrument never will.

The calculator below does both jobs luthiers actually need. Single fret gives the exact distance from the nut to any fret, with the remaining distance to the bridge and the slot spacing. Full fretboard lays out the entire board in one table. Presets cover the six most common scale lengths, rounded to the nearest millimetre, and everything works in millimeters or inches.

Quick Answer

The equal-temperament formula behind every fret

The formula is short: distance from the nut to fret n equals scale length minus scale length divided by 2 raised to n over 12. The 2 raised to 1 over 12 is the twelfth root of two, about 1.059463, which is the frequency ratio of one semitone in equal temperament, the system underpinning modern western tuning. Each fret shortens the remaining string by that same ratio, so twelve frets halve the string and raise the pitch by exactly one octave.

That halving is the whole sanity check in one line. At fret 12, 2 raised to 12 over 12 equals 2, so the formula gives scale minus scale over 2, which is half the scale. At fret 24, two octaves up, it gives three quarters of the scale, leaving one quarter to the bridge. If a table you find elsewhere disagrees with those two landmarks, the table is wrong, whatever its other rows say.

Builders often meet the same math in a second form: the Rule of 17.817. Divide the scale length by 17.817 and you get the first fret position, then divide the remaining length by 17.817 again for each next fret. StewMac states the factor as 17.817154 and describes exactly that repeated division. It is the same formula, not a rival one: 17.817 is 1 divided by (1 minus 2 to the power of negative 1 over 12). Use whichever form you trust, but do not mix them halfway down the board.

Worked examples for three real instruments

Three checks you can run against the calculator right now, each verified by hand. First, the prefilled electric guitar: scale 648 mm, fret 12. The formula gives 648 minus 648 over 2, which is 324.00 mm from the nut, with 324.00 mm left to the bridge and a 19.27 mm gap from the 11th fret. Second, a classical guitar: scale 650 mm, fret 3. The formula gives 650 minus 650 over 2 to the power of 3 over 12, which is 103.42 mm from the nut, with 546.58 mm left to the bridge and a 32.50 mm gap from the 2nd fret. Third, a bass guitar: scale 864 mm, fret 5. The formula gives 864 minus 864 over 2 to the power of 5 over 12, which is 216.73 mm from the nut, with 647.27 mm left to the bridge and a 38.49 mm gap from the 4th fret.

In inches, the same math holds with no conversion tricks. A 25.5 inch scale puts the first fret at 1.43 inches and the 12th at 12.75 inches. That inch example is worth memorizing, because it exposes the most common error in other tools: some pages show scale divided by 2 to the power of n over 12, which is the string length remaining to the bridge, and label it as the distance from the nut. For fret 1 on a 24.75 inch scale that remaining length is 23.36 inches, which is plainly not where the first fret goes. The correct nut distance is the scale minus that figure, 1.39 inches. If a tool answer looks like most of the scale length for a low fret, it has shown you the wrong end of the string.

Common scale lengths and where each fret lands

Scale length is the one input that decides everything, so measure it properly: the vibrating length from the nut to the bridge saddle. If you only know the nut-to-12th-fret distance, double it, or use a scale length calculator to work it out from your measurements. Do not measure to the end of the bridge plate or to a saddle that has already been compensated forward, or every fret will inherit that error.

Instrument (preset)	Scale	Fret 1 from nut	Fret 12 from nut	Fret 24 from nut
Fender guitar	648 mm	36.37 mm	324.00 mm	486.00 mm
Gibson guitar	629 mm	35.30 mm	314.50 mm	471.75 mm
PRS guitar	635 mm	35.64 mm	317.50 mm	476.25 mm
Bass guitar	864 mm	48.49 mm	432.00 mm	648.00 mm
Classical guitar	650 mm	36.48 mm	325.00 mm	487.50 mm
Tenor ukulele	432 mm	24.25 mm	216.00 mm	324.00 mm

The presets are rounded to the nearest millimetre: a true Fender scale is 647.7 mm and a true Gibson scale is 628.65 mm, so a preset result can differ from a spec-sheet calculation by a fraction of a millimetre. For a build, enter your measured scale rather than trusting a preset name, since individual instruments vary by year and setup. The same table works for mandolin, banjo, and any other fretted instrument: only the scale length changes, because equal temperament governs them all. The Simon Fraser University handbook states the semitone ratio plainly as the twelfth root of two, and notes that only the octave remains a pure interval in this system.

Cutting slots without compounding error

The practical rule is simple to state and easy to violate: mark every slot position from the nut, in one direction, from a single zero point. The table slot-spacing column tells you the gap between neighboring frets, which is useful for checking a cut, but if you lay out a board by stepping gap after gap, each small marking error carries into every later fret. By fret 24 those errors are audible. Measure from the nut, check the 12th fret against half the scale before cutting anything, and work to 0.1 mm or 0.005 inches on the first several frets, where a small absolute error shifts pitch most.

Then accept the limit of the theory. Equal temperament assumes a perfect string with no stiffness and no stretch, and real strings have both, which is why even a perfectly slotted board needs saddle compensation: the saddle is typically set a couple of millimetres beyond the theoretical scale length, more for thicker strings and higher action. That adjustment belongs at the bridge, and it does not change where the frets go. If a guitar plays sharp up the neck after correct slotting, suspect the saddle position and the nut height before doubting the fret math. Once the frets are placed, a guitar chord calculator is a handy check that the shapes you play land where your fingers expect them.

Single fret or full fretboard: which mode to use

Use single fret when you are checking, replacing, or repairing one position: a worn slot, a suspect measurement, or a conversion from inches. Use the full fretboard table when you are laying out a new board, because it gives you every position, every remaining length, and every gap in one pass, and the 12th-fret row lets you verify the whole table at a glance. The board mode tops out at 24 frets, which covers almost every production guitar, while single mode runs to fret 36 for extended-range builds and for checking a position beyond the board end.

One more distinction is worth keeping straight. This tool positions frets; it does not voice the instrument. Fret wire size, neck relief, action height, and string gauge all change how a guitar feels and how it intonates in practice, but none of them change the theoretical fret positions. Keep those jobs separate: slots from this calculator, setup from measurements on the finished instrument.

What competing calculators miss

The best-known fret tool computes only the first fret, which answers a question almost nobody asks on its own. The one rival with a full table has no quick single-fret mode and no inch output for a fixed board, and at least one popular page labels the remaining string length as the nut distance, which sends a first fret to the wrong end of the neck. This calculator keeps the fast single-fret answer, adds the complete fretboard table with slot spacing and fret-to-bridge distances, works in millimeters or inches, and ships the six scale lengths builders actually reach for. A built-in 12th-fret sanity check catches unit mix-ups before they reach the workbench, and the reset button returns the tool to the worked example instead of leaving blank fields behind.

Frequently asked questions

Add This Calculator to Your Website

References