Kato Unitrack is designed around a 33 mm (1.2992 inch) track center-to-center. Using various changes in geometry you can also make 49.5 mm (1.9488 inch) and 66 mm (2.5984 inch) centers. You can see the 33 mm center-to-center in the curved track segment radii which increase in 33 mm increments, the double crossover tracks having a 33 mm center-to-center, and the double track pieces having a 33 mm center-to-center.
The examples shown below are applicable to both EP481-15L left #4 turnouts (Kato #20-220) and EP481-15R right #4 turnouts (Kato #20-221). The “481” in the numbers represents a 481 mm (18.937 inch) radius and the “15” represents a 15° segment.
The #4 turnout packages include a 60 mm cut-corner straight piece (S60L and S60R), a 64 mm straight piece (Kato #20-030), and an R481-15 curve piece (Kato #20-160).
The straight segment of the #4 turnout is 126 mm, 2 mm longer than the 124 mm straight piece. In the second example below you’ll see a 62 mm (Kato #20-040) and 64 mm piece added to make the track ends even. The curved segment of the #4 turnout is the same size as the R481-15 curve piece.
If you understand the geometry of the #4 turnout laying out the Unitrack pieces is much easier.