This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
1. Take the sum of two risers and subtract it from 24 inches; the result will be the width of the tread. This rule is based on the assumption that an average step is 2 ft. and that the labor of lifting the foot vertically is twice that exerted in moving horizontally, consequently the width of the tread, added to twice the height of the riser, should be equal to 2 ft.
2. The first column of the accompanying table gives the width of treads; the other gives the corresponding height of risers.
3. The product of the tread and risers should equal 66 inches: thus, with a tread of 11 in. the riser would be 6 in.; with a riser of 7 in., the tread would be 9 3/7 in.
The following method is of service in obtaining the accurate bevel to apply on the edge of a stair stringer, where it is desired that the riser miter with the stringer, as in an open string stairway. By the use of the pitch board, mark on the outside face of the stringer the cuts for the treads and risers, as in Fig. 23. Draw b e parallel to a d,
and at a distance t from ad equal to the thickness of the stringer. At b, draw b c square across the upper edge of the stringer, and connect c and a. Then bac is the miter bevel required. At a' is shown a bevel set to the line obtained, so that it can be used at all the other riser lines.