Luthiery Laboratories

Here is a spreadsheet of fret positions, mainly Fender, but others also:

StewMac has an online fret position calculator: https://stewmac.com/FretCalculator

The mathematical formula is:

where

• x = fret distance from inside of nut
• S = scale length
• n = fret number ( 0 = nut, 12 = octave )

I actually used a caliper accurate to thousandths of an inch to mark the locations, and pre-punched them with a new sharp punch prior to drilling. I probably got an accuracy of under 1/100", which is fine for a fretted instrument on which all tuning is approximate anyway.

Two spots you can know with good accuracy are the nut ( 0" ) and the octave ( 1/2 scale length ). Working in both directions from those datums, you can cover almost the entire neck with direct measurements using a 6" caliper.

All these measurements are typically done in inches, but there is no reason you could not use millimeters or barleycorns or cubits or any other silly system.