Length of the skirt (skirting) board along the rake, plus the plumb and level cut angles at the ends.
The skirt board runs along the open or wall side of a stair, parallel to the stringer. Its length is the rake; the end cuts are a plumb (vertical) cut and a level (horizontal) cut set by the stair angle.
A finish board that runs along the side of a staircase, covering the rough stringer and the joint where treads meet the wall.
The plumb (vertical) cut equals the stair angle from horizontal; the level (horizontal) cut is 90 degrees minus that angle.
At least the diagonal rake length of the flight, plus a little for the end cuts.