Fret Calculator — Guitar Fret Position
Find the precise position of any fret on a guitar, bass, or other stringed instrument. Enter the scale length (nut to bridge) and the target fret number to get the exact distance from the nut and the remaining vibrating string length.
mm
Measured along the string from the nut to the centre of the fret wire
- 1
Length factor at fret
2^(−12 ÷ 12) = 0.5Pressing at fret n shortens the vibrating string to L × 2^(−n/12), raising pitch by n semitones. - 2
Fractional distance from nut
1 − 0.5 = 0.5 - 3
Nut-to-fret distance
648 × 0.5 = 324
此計算機如何運作？
Fret n sits at D = L × (1 − 2^(−n/12)) from the nut, where L is the scale length. The 12th fret is always at L/2. Fret spacing narrows logarithmically toward the body because equal semitone steps correspond to equal frequency ratios, not equal distances.
公式
How this is calculated
Western equal temperament divides the octave into 12 equal semitones, each a ratio of 2^(1/12) ≈ 1.0595 relative to the previous. Pressing a string at fret n shortens the vibrating length to L / 2^(n/12), raising the pitch by n semitones. The nut-to-fret distance is therefore D_n = L − L / 2^(n/12) = L × (1 − 2^(−n/12)).
This geometric series gives the classic "rule of 18": fret 1 sits at approximately L / 17.817 from the nut, fret 2 at L / 17.817 of the remainder, and so on. Every 12th fret is exactly at half the scale length (one octave higher). The spacing between consecutive frets narrows exponentially toward the body.
The calculation assumes a perfectly straight string with zero action and compensation. In practice, luthiers add a small amount of saddle compensation (typically 1–3 mm) to correct for the sharpening effect of string deflection when fretting — this calculator gives the theoretical fret slot positions, which are accurate to within fractions of a millimetre for standard builds.
常見問題
Fender electric guitars use 648 mm (25.5 in), Gibson electrics use 628–629 mm (24.75 in), and most Martin dreadnoughts use 645 mm (25.4 in). Bass guitars are typically 864 mm (34 in).
12 semitones equal one octave, and an octave doubles the frequency. To double frequency you halve the vibrating string length, so fret 12 sits at exactly L/2 regardless of scale length.
The formula gives the theoretical node point — the centre of where the fret wire contacts the string. Slot position is very slightly toward the nut (by half the fret wire width), but for all practical luthiery and measurement purposes the difference is negligible.
也稱為
TG we-Calculate Editorial Team. (2026). Fret Calculator — Guitar Fret Position [Online calculator]. TG we-Calculate. https://we-calculate.com/zh-tw/calculator/fret-calculator
TG we-Calculate Editorial Team. "Fret Calculator — Guitar Fret Position." TG we-Calculate. 2026. https://we-calculate.com/zh-tw/calculator/fret-calculator.
TG we-Calculate Editorial Team, "Fret Calculator — Guitar Fret Position," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/zh-tw/calculator/fret-calculator
@misc{wecalculate_fret_calculator, title = {Fret Calculator — Guitar Fret Position}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/zh-tw/calculator/fret-calculator}}, year = {2026}, note = {TG we-Calculate} }
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