How to use the Stair Calculator
- Measure finished floor to finished floor, then enter your maximum riser height and going per tread.
- Add the available straight run and compare riser counts. Select a row to update the elevation.
- If measured, enter the floor opening and floor thickness to estimate vertical headroom at the opening edge.
- Record site notes, save the project and export a measurement brief with the stair elevation.
Compare stair layouts before cutting
Adding a riser lowers each step but usually lengthens the flight. This stair calculator compares both against the constraints you enter. A 108-inch floor-to-floor rise and a 7.75-inch maximum gives 14 risers of 7.714 inches. When the upper floor forms the last step, there are 13 treads. At a 10-inch going, total run is 130 inches.
How stair rise and run are calculated
Divide the total rise by the riser count to get equal riser heights. Multiply the tread count by the going to get total run. The geometric diagonal is the square root of rise squared plus run squared. Nosing projection is recorded separately: the going is already measured between successive nosings.
Check the opening with measured headroom
For a horizontal upper-floor soffit, the planner estimates clearance from the straight pitch line at the opening edge. Enter the opening length measured back from the upper landing and the full floor thickness. It does not inspect sloped ceilings, beams or other obstructions. The sketch records a planning estimate, not a site inspection.
Your limits, kept with the project
The initial 7.75-inch riser, 10-inch going and 80-inch headroom target are editable starting values, not a code compliance result. Local requirements depend on the building and stair type. Check the requirements for your project before using a layout. Stringer support, board depth, connections, guards, landings and structural capacity are outside this geometry tool.