The method provides luthiers of fretted instrument with a novel approach for installing frets with increased accuracy. The method is an improvement in calculation of fret placement over the “Rule of 18” because it relies on the length of the vibrating string. This method is more pronounced at the end of the fret board closest to the bridge due to the angle formed by the string when depressed with respect to the axis of the fret board. With respect to the twelve-step octave, the scale length is multiplied by the constant of the twelfth root of 0.5 to calculate the length of the string from fret contact to saddle contact for the next tonal step.