Initial data
The height of the stairs 2.5 m     (2500 mm)
The length of the stairwells in the plan 3000 mm
Number of steps 13
The thickness of the treads 50 mm
Tread Overhang 50 mm

Stringer
The length of the bowstring 4167 mm
The angle of the stairs 39.8°

Step size
Step height 192 mm
Depth steps 281 mm
The height of risers 142 mm