How to Measure Stairs

A stair calculation should begin with finished elevations and the space available for the run. Equal risers and treads are a layout goal; local rules add requirements for landings, headroom, handrails, nosings, and guards.

Measure finished floor to finished floor

Measure vertically from the finished lower surface to the finished upper surface. Account for flooring, tile, nosings, and any finish that changes the walking surfaces. Rough framing dimensions are not the final stair rise.

Choose a target, then calculate actuals

Enter a maximum or target riser to calculate a whole number of risers. Divide total rise by that count to get the actual equal riser, then multiply the number of treads by tread depth for total run. A different target may produce a more workable layout.

The calculator’s angle and stringer length describe geometry. They do not establish that the stair is permitted or safe in your jurisdiction.

Check the space

Compare the calculated run with the available floor area. Then check landings, headroom, handrails, guards, nosing projection, width, and transitions. Local residential rules vary; OSHA references below are workplace/construction references, not universal residential code.

Build only from a reviewed layout

Stairs are a fall hazard during construction. Use temporary protection, keep the route clear, and have structural connections and code questions reviewed by the appropriate professional or authority.

Worked examples