Important stairway measurements.

  • The rise height or rise of each step is measured from the top of one tread to the next. It is not the physical height of the riser; the latter excludes the thickness of the tread. A person using the stairs would move this distance vertically for each step he takes.
  • The tread depth of a step is measured from the edge of the nosing to the vertical riser; if the steps have no nosing, it is the same as the going; otherwise it is the going plus the extent of one nosing.
  • The run/going of a step is measured from the edge of the nosing to the edge of nosing in plan view. A person using the stairs would move this distance forward with each step they take.
  • To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
  • The total run or total going of the stairs is the horizontal distance from the first riser to the last riser. It is often not simply the sum of the individual tread lengths due to the nosing overlapping between treads. If there are N steps, the total run equals N-1 times the going: the tread of the last step is part of a landing and is not counted.
  • The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning. If there are 14 steps, the total rise equals 14 times the rise of each step for example.
  • The slope or pitch of the stairs is the ratio between the rise and the going (not the tread depth, due to the nosing). It is sometimes called the rake of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads.
  • Headroom is the height above the nosing of a tread to the ceiling above it.
  • Walk-line – for curved stairs, the inner radius of the curve may result in very narrow treads. The "walk-line" is the imaginary line some distance away from the inner edge on which people are expected to walk. Building code will specify the distance. Building codes will then specify the minimum tread size at the walk-line.

  • Ergonomically and for safety reasons, stairs must have certain measurements so that people can comfortably use them. Building Codes typically specify certain measurements so that the stairs are not too steep or narrow. In the U.S.A  building codes, while varying from State to State and County to County, generally specify the following parameters:.

  • Minimum tread length, typically 9 inches (229 mm) excluding the nosing for private residences. Some building codes also specify a minimum riser height, often 5 inches.
  • Riser-Tread formula: Sometimes the stair parameters will be something like riser plus tread equals 17–18 inchesanother formula is 2 times riser + tread equals 24.6 inches the length of a stride. Thus a 7 inches rise and a 10.6 inches tread exactly meets this code. If only a 2 inches  rise is used then a 20.6 inches tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer.
  • Low rise stairs are very expensive in terms of the space consumed.
  • Slope: A value for the rise-to-tread ratio of 17/29 ˜ 0.59 is considered optimal; this corresponds to a pitch angle of about 30°.
  • Variance on riser height and tread depth between steps on the same flight should be very low. Building codes require variances no larger than 0.1875 inches (4.76 mm) between depth of adjacent treads or the height of adjacent risers; within a flight, the tolerance between the largest and smallest riser or between the largest and smallest tread can not exceed 0.375 inchesThe reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly by the subfloor. If thick flooring (e.g. thick hardwood planks) are added on top of the subfloor, it will cover part of the first riser, reducing the effective height of the first step. Likewise at the top step, if the top riser simply reaches the subfloor and thick flooring is added, the last rise at the top may be higher than the last riser. The first and last riser heights of the rough stairs are modified to adjust for the addition of the finished floor.
  • Maximum nosing protrusion, typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
  • Height of the handrail. This is typically between 34 and 38 inches (864 and 965 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 38 inches for residential applications and 42 inches for commercial railings.
  • Handrail diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches
  • Maximum space between the balusters of the handrail. This is typically 4 inches
  • Openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches
  • Headroom: At least 83 inches
  • Maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
  • Mandate handrails if there is more than a certain number of steps (typically 2 risers)
  • Minimum width of the stairway, with and without handrails
  • Not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
  • A stairwell may be designated as an area of refuge as well as a fire escape route.