Stair railings serve as a safety feature as well as an aid for people climbing stairs, but they must be sized and angled correctly to meet building codes and to allow safe and comfortable use. You can work out the stair rail angle from the slope or angle of the stairs. One method used to determine this angle is the triangle or Pythagorean theorem, which is a formula used to measure the angled side of a right triangle. A simpler method for calculating the rail angle is by measuring vertically at the top and bottom of the staircase.
Place a 91 cm (36 inch) mark on the level by measuring from the end, marking it on both edges of the level.
Place the level vertically on the bottom tread of the stairway, at the nosing. The nosing is the rounded, front area of the stair tread.
Plumb the level by aligning the bubble in the centre of the two vial marks.
Place a pencil mark horizontally on the wall at the 91 cm (36 inch) mark of the level and mark the vertical side of the level, forming two intersecting lines.
Place the level vertically on the nosing of the upper stair landing and mark the wall in the same manner as the bottom tread.
Stretch the chalk line from the top intersecting marks to the bottom intersecting marks and snap the line.
Place the level horizontally on the wall at the bottom stair intersecting line.
Mark a line horizontally, across the intersecting line.
Place the protractor on the wall by aligning the flat side on the horizontal line and centre the base of it on the vertical line.
Determine the angle by reading the protractor on the degree marks, where the chalk line intersects the radius of the protractor.
If working on a finished wall surface, apply masking tape to the wall where the marks will be made.