There are internal building codes for stair dimensions within a home, to comply with residential regulations. These must be followed accurately when building new staircases.
A stair tread must be no less than 11 inches in width. This is to allow enough of the foot to be on the stair and prevent falling. The vertical tread can be no less than 7 inches and no greater than 7 1/4 inches. With regard to headroom above the stairs, the minimum clearance is 6 feet 8 inches. If you are unsure with regard to your own State or local area codes, talk to your building regulations office for clear and concise advice.
There is no legal definition of the amount of stairs there should be in one single stair case flight. However, the total measurements from bottom to top must no exceed 12 feet. If you have a landing, it must not be smaller than 36 inches wide, but there is no limit to the length, (providing it is no less than 36 inches also).
Balusters and Railings
There should be one baluster or rail for every stair tread and the gap between the balusters must not exceed 4 inches. These are general measurements for a national code, but your own local area may differ. Seek advice before installing a home stair case.