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Stair Calculator To Work Out Run and Rise Lengths, Free Online Tool

Use our easy calculator to work out the rise and run (going) lengths of straight length stairs.

Article By: Tom Ayre | Last Update: November 2020

When designing or redesigning a set of stairs there can often be some confusion with regards to number of stairs, height and length of stair. Often you need to sit down and really think about the design to ensure that everything fits and is up to standard! We recommend undertaking a thorough measured survey of the area to ensure everything you are designing will fit!

Using our free stair calculator below you will be able to:

  • Stair run length
  • Stair run length with nosing
  • Stair rise length
  • Elevation angle (in degrees)

Have a look at the calculator below.

Stair Calculator Terminology

Elevation Angle
Angle of stairs from horizontal in degrees.

O/A Rise Length
Overall vertical distance between floor levels.

O/A Run Length 
Overall horizontal distance between start and end of the stair.

Rise Length
Vertical distance between the stair and next stair.

Run / Going
Horizontal distance from the end of the previous stair and start of next.

Terminology Diagram

Stair Run and Rise Diagram

Stair Calculator

Stair Standards

The latest standards document we could find is Approved Document K from 2013. This can be found here.

Please double check the information for yourself before you commit to any designs!


Private Stairs

Min Rise (mm) = 150 mm
Max Rise (mm) = 220 mm
Min Going (mm) = 220 mm
Max Going (mm) = 300 mm

Utility Stairs

Min Rise (mm) = 150 mm
Max Rise (mm) = 190 mm
Min Going (mm) = 250 mm
Max Going (mm) = 400 mm

General Access Stairs

Min Rise (mm) = 150 mm
Max Rise (mm) = 170 mm
Min Going (mm) = 250 mm
Max Going (mm) = 400 mm

Max Elevation Angle = 42º

Other Requirements:

  • For school buildings, the preferred rise is 150 mm and the preferred going is 280 mm.
  • For dwellings, for external tapered stairs that are part of the buildings, the going should be a minimum of 280 mm.
  • For existing buildings, alternatives may be proposed if the dimensional constraints do not allow these requirements to be followed.
  • There are more complex requirements for stepped gangways in assembly buildings, and there may be a conflict between these requirements and sightlines in some buildings with spectator seating.
  • Buildings that are not dwellings and common areas in buildings that contain flats should not have an open riser, should have visual contrast to make nosings apparent, and nosings should not protrude by more than 25 mm.
  • The minimum headroom should be 2 m.