This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
In setting out a stairway, the first consideration should be to ascertain the exact height between the floors, the height to be measured from the top of the floor below to the top of the floor above. For this purpose, a rule or rod is sometimes used, termed a story rod, on which the whole number of risers is to be marked. Care should be used in determining the risers, with the view of constructing a stairway having steps of convenient height. Experience teaches that between 6 inches and 7 inches rise is the limit of easy stepping; therefore, the total height of the story rod should be divided by either one of these numbers, which will give the number of risers required. Having in this manner ascertained the number needed, divide it into the height of the story rod; the quotient will be the exact height of each riser.