read this

 

INTERNATIONAL RESIDENTIAL CODE (IRC)

The International Residential Code dictates stair code requirements specific to residential buildings. The IRC stairs code states that, to comply with stairway requirements, the minimum width for residential stairs be no less than 36 inches. The stair riser code is up to 7.75 inches, and can not vary more than 3/8 of an inch. There are also section codes in place for standard stair tread dimensions. The tread depth code for residential stairs should be no less than 10 inches with nosing, no less than 11 inches without nosing, and maximum tread depth variation should also be less than 3/8 of an inch.

 

 And the spacing between handrail brackets should be about 3 ft.