Fret Position Calculator
Enter your instrument scale length to see the exact position of every fret under equal temperament. Get the distance from nut to each fret, the remaining distance to the bridge, and the gap between adjacent frets - useful for custom guitar and bass builds, fret replacement, and intonation setups. Switch between millimetres and inches. Presets cover the most common guitar and bass scales.
Formula
Worked example
For a Fender Stratocaster with a 647.7 mm (25.5 in) scale length, fret 1 is at 647.7 × (1 - 2^(-1/12)) ≈ 647.7 × 0.0561 ≈ 36.35 mm from the nut. Fret 12 is at exactly 647.7 / 2 = 323.85 mm. Fret 24 is at 647.7 × (1 - 2^(-24/12)) = 647.7 × 0.75 = 485.78 mm.
How fret positions are calculated
Every modern stringed instrument uses equal temperament, a tuning system in which each semitone is separated by a ratio of the 12th root of 2 (approximately 1.059463). Because pitch is determined by the ratio of a string length to its total scale length, each fret divides the remaining string by this same factor. The formula for the distance from the nut to fret n is: distance = scale length x (1 - 2^(-n/12)). The 12th fret always lands at exactly half the scale length, which is the octave of the open string. This is the most useful sanity check when building or measuring a fretboard: if the 12th fret is not at half the scale length, the fret placement is wrong.
Scale length and its effect on tone and playability
Scale length is the distance from the nut to the bridge saddle. A longer scale produces tighter string tension at a given pitch, which makes the tone brighter and the feel stiffer. A shorter scale produces looser tension, a warmer tone, and an easier fretting hand for chords and bends. Standard electric guitars range from 24 inches (Fender Jaguar) to 25.5 inches (Fender Stratocaster). Gibson-style guitars sit at 24.75 inches - a difference of less than an inch that players notice immediately. Bass guitars typically use 34 inches (standard) or 35 inches (long scale for 5-string instruments). Classical guitars are typically 650 mm. Baritone guitars, tuned lower than standard, use scales from 27 to 30 inches.
Using fret positions in a build or repair
When cutting new fret slots, work from the nut toward the body. Mark each slot position from the nut, not from the previous slot, so that small errors do not accumulate. After slotting, measure the 12th fret from the nut and compare it to half the scale length: any discrepancy greater than 0.5 mm will affect intonation noticeably. The slot width (gap column in the table below) shrinks toward the high frets - on a 25.5 in guitar the gap at fret 1 is about 36 mm while fret 24 is only about 8 mm. Fret spacing also informs nut placement: the nut should sit so that the open-string length exactly equals the scale length you have calculated.
Multiscale and fan-fret instruments
Fan-fret (multiscale) guitars use a different scale length for the bass strings than for the treble strings. The fret positions on each side are calculated independently using the same formula, but the slots are cut at an angle across the fretboard so they land at the correct position for both scales simultaneously. One fret (the "perpendicular fret") is typically kept straight across the neck; all others fan. To calculate a multiscale layout, run this calculator twice - once for the bass scale and once for the treble scale - then interpolate the slot positions across the fretboard width.
Common instrument scale lengths
| Instrument | Scale length (mm) | Scale length (in) | 12th fret (mm) |
|---|---|---|---|
| Fender Stratocaster / Telecaster | 647.7 | 25.5 | 323.85 |
| Gibson Les Paul / SG | 628.65 | 24.75 | 314.33 |
| PRS Custom 24 | 635 | 25.0 | 317.50 |
| Fender Jaguar / Mustang | 609.6 | 24.0 | 304.80 |
| Baritone guitar | 685.8 | 27.0 | 342.90 |
| Electric bass (short scale) | 762 | 30.0 | 381.00 |
| Electric bass (standard) | 863.6 | 34.0 | 431.80 |
| Electric bass (long scale) | 889 | 35.0 | 444.50 |
| Classical guitar | 650 | 25.6 | 325.00 |
| Ukulele soprano | 345 | 13.6 | 172.50 |
| Ukulele tenor | 432 | 17.0 | 216.00 |
Nominal scale lengths for popular guitars, basses and ukuleles. Actual measurements may vary slightly by manufacturer.
Frequently asked questions
What is scale length on a guitar?
Scale length is the distance from the inside edge of the nut (where the string leaves the nut) to the contact point on the bridge saddle. It determines string tension at pitch and controls where every fret must sit. A longer scale length means frets are spaced farther apart and strings feel stiffer. Most electric guitars are between 24 and 25.5 inches.
Why is the 12th fret always at half the scale length?
In equal temperament, each octave represents a 2:1 frequency ratio. To double the frequency of a string, you halve its vibrating length. Fretting at the 12th fret shortens the string to exactly half the open length, producing the octave. Because of this, the 12th fret position is the simplest way to verify that a fretboard has been correctly slotted: measure nut to 12th fret and compare to half the scale length.
What is the "rule of 18" and how does it differ from this calculator?
The historical "rule of 18" is an approximation of the equal-temperament formula that divides the remaining string length by 18 at each fret. The exact constant is 17.817154, not 18. Using 18 overstates fret spacing slightly, so the 12th fret lands a little flat. This calculator uses the mathematically exact 12th root of 2, which is standard for all modern fret work.
How do I measure the scale length of an existing guitar?
The most accurate method is to measure from the nut to the 12th fret, then double that number. The 12th fret must be exactly at half the scale length for the instrument to be in tune across the neck. You can also measure directly from the nut to the bridge saddle, but saddle position varies slightly for intonation compensation so doubling the 12th-fret measurement is more reliable.
Why do fret spaces get narrower toward the body?
Each fret divides the remaining string by the same ratio (the 12th root of 2), so every successive fret is a smaller absolute distance from the previous one. At fret 1 on a 25.5 in guitar, the gap is about 36 mm. By fret 12 the gap is about 18 mm, and at fret 24 it is only about 9 mm. This exponential shrinking is a direct consequence of the ratio-based frequency math.
What units should I use when slotting frets?
Luthiers generally prefer millimetres because fret-slot saws and templates are calibrated in metric and because thousandths-of-a-millimetre precision is easy to express. Imperial measurements in inches require fractional notation that is harder to read at a glance. This calculator supports both - switch to inches if you are working from an imperial-spec template.
Can I use this calculator for a bass or ukulele?
Yes. The equal-temperament formula is the same for every fretted instrument regardless of size. Select the appropriate preset (bass 34 in, bass 35 in, ukulele soprano, ukulele tenor) or enter a custom scale length for any other instrument.