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Fret Calculator

Building a stringed instrument requires exact fret placement to ensure proper pitch and intonation. This calculator computes fret positions along the fingerboard based on the equal temperament tuning system used in Western music. Luthiers, DIY guitar builders, and instrument makers use these measurements to position metal frets accurately. Input your scale length—the distance from nut to bridge—and receive distances from the nut for all 27 frets.

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Creators Jasmine J. Mah, BSc
4,264 people find this calculator helpful

Understanding Frets and Equal Temperament

Frets are metal strips embedded perpendicular to the fingerboard on guitars, ukuleles, banjos, and similar instruments. Each fret divides the string into segments; pressing a string against a fret shortens the vibrating length and raises the pitch. The spacing between frets is not uniform—they follow a logarithmic progression derived from the equal temperament scale, the tuning standard adopted across modern Western music.

This system ensures that each semitone increment maintains a consistent frequency ratio, allowing an octave to be divided into 12 equal steps. The mathematical relationship underpinning fret placement dates back centuries and combines principles from acoustics and frequency theory. Proper fret spacing is essential; even millimetre deviations can produce noticeable intonation problems, particularly in upper registers.

The Fret Position Formula

The distance from the nut to any given fret is calculated using the equal temperament formula. This accounts for the exponential nature of frequency perception and ensures chromatic accuracy across the entire fingerboard.

Distance to fret n = Scale Length × (1 − (2^(−n/12)))

Or equivalently:

Distance to fret n = Scale Length × (1 − (1/(2^(1/12)))^n)

  • Distance to fret n — Distance from the nut to fret number n, measured in the same units as scale length
  • Scale Length — The distance between the nut and bridge of your instrument (typically 63.5 cm or 25 inches for standard guitars)
  • n — The fret number (1, 2, 3, ... up to 27)
  • 2^(1/12) — The equal temperament semitone ratio, approximately 1.05946

Scale Length and Its Role

Scale length is the vibrating portion of the string and directly determines all fret positions proportionally. A longer scale produces longer strings, which generally yield a brighter tone and increased string tension; a shorter scale offers easier playability and warmer tones. Standard electric guitars typically measure 24–25.5 inches (61–65 cm), while acoustic guitars often reach 25.5–26 inches (65–66 cm). Bass guitars exceed 30 inches (76 cm), whilst ukuleles range from 20–23 inches (51–58 cm).

Your chosen scale length is the first input required. Accuracy here is critical; a 1 cm error in scale length propagates across every subsequent fret position. Always measure from the inside of the nut to the inside of the bridge saddle, or use the manufacturer's specification for known instrument models.

Reading and Applying the Results

Once you enter your scale length, the calculator displays the distance from the nut to each fret. These measurements allow you to mark and rout fret slots precisely. Use a straightedge or fret jig to ensure straight lines along the fingerboard, then measure from the nut using callipers or a ruler graduated in millimetres for maximum accuracy.

The 12th fret occupies exactly half the scale length—a useful checkpoint. If your measured 12th fret position deviates significantly from this midpoint, re-examine your scale length input and initial measurements. Modern lutherie often employs CNC routing for consistency, but hand methods work well with careful measurement and layout.

Practical Fret Layout Tips

Avoiding common mistakes ensures your instrument plays in tune across the entire neck.

  1. Account for Tool Width — Fret saw blades and routing bits remove material as they cut. If you measure slot centres, adjust your measurements by half the bit diameter on either side of the calculated position. Precision here prevents sharp or dead frets.
  2. Verify Scale Length Before Starting — Confirm your scale length matches your design intent. Some builders specify scale from the nut to the 12th fret (half scale) to avoid bridge saddle geometry complications. Measure twice, mark once.
  3. Use Reference Points — Mark the 1st, 12th, and final fret first, then fill intermediate frets. This three-point check catches errors early. If your 12th fret is off-centre, recalculate from scratch rather than adjusting subsequent slots.
  4. Allow for Fret Crown and Action — The formula gives slot positions, but fret crown height and string action vary by design. After fret installation, levelling and crowning adjust playability independently of slot position. Budget time for this finishing stage.

Frequently Asked Questions

Why are frets spaced closer together towards the body of the guitar?

Fret spacing follows an exponential decay pattern because musical pitch perception is logarithmic. Each semitone represents a constant frequency ratio (the 12th root of 2), not a constant frequency difference. This means the physical distance required to produce a pitch increment shrinks as you move away from the nut. Early frets are widely spaced; later frets compress toward the bridge, reflecting how our ears perceive pitch intervals.

What is the 12th fret rule, and why is it important?

The 12th fret is always positioned exactly halfway along the scale length. This occurs because doubling frequency (one octave) corresponds to halving string length in acoustics. It serves as an excellent verification checkpoint when laying out frets. If your 12th fret measurement does not land at the scale length midpoint, your scale length input or prior measurements contain an error. Catching this early saves significant rework.

Can I use these measurements for instruments other than guitars?

Yes. The equal temperament formula applies to any Western string instrument with a fingerboard—ukuleles, mandolins, banjos, bass guitars, and even some traditional instruments adapted to equal temperament. Scale length varies by instrument type, but the mathematical relationship between scale and fret position remains identical. Always confirm your target instrument's scale length specification before starting.

How accurate do fret positions need to be?

Professional tolerance is typically ±0.5 mm, though ±1 mm is acceptable for amateur builds. Errors beyond 1 mm become audible as intonation problems, especially in higher registers where fret spacing is tight. Electronic callipers and a quality straightedge help achieve this precision. Hand marking and hand routing can match this tolerance with care; CNC routing consistently exceeds it.

Does scale length affect the spacing pattern between consecutive frets?

No. The ratio between any two adjacent frets remains constant regardless of scale length. If you scale a 25-inch fingerboard layout to 24 inches, every fret position shrinks proportionally, but the gaps between them maintain the same percentage relationships. This is why the equal temperament formula is scale-invariant—it depends only on fret number, not absolute scale length.

Why is equal temperament used instead of just fine-tuning with machine heads?

Equal temperament is a compromise that allows an instrument to play acceptably in all keys. Just intonation (based on pure frequency ratios) sounds perfect in one key but noticeably out-of-tune in others. By locking fret positions to equal temperament, you fix intonation uniformly across the fingerboard. Machine heads then handle fine-tuning and compensation for stretching, action differences, and minor manufacturing variance.

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