The formula to calculate the scale length (SCL) is:
\[ SCL = F \times FTFD \]
Where:
Let's say the number of frets is 20 and the fret-to-fret distance is 1.5 inches. Using the formula:
\[ SCL = 20 \times 1.5 \]
We get:
\[ SCL = 30 \]
So, the scale length (\( SCL \)) is 30 inches.