Stairways shall not be less than 36 in. in clear width at all points above the permitted handrail height and below the required headroom height.
The International Residential Code (IRC) governs the maximum rise (the height of each step) and the minimum run (the depth of each step), which are 7-3/4 in. and 10 in., respectively. Many jurisdictions, particularly in the Northeast, allow an 8-1/4-in. rise and a 9-in. run.
Treads on stairs with a run of less than 11 in. must overhang the riser below by a minimum of 3⁄4 in. and a maximum of 1-1/4 in.; so tread depth is actually larger than the run.
Sources suggest that when finding the overall rise, you should measure from the finished floor at the bottom of the stairs to the finished floor at the top.
If the finished floor isn’t in place, measure from the subfloor, adding the thickness of the upper flooring and subtracting the thickness of the bottom flooring. If the finished floor won’t be in place when you install the stringers, add its thickness to the height of the bottom riser, or shim the stringers.
Find out more about laying out basic stair tringers at Finehomebuilding.com.
Get unique ideas for decorating your staircase at Housebeautiful.com.