Stair Rise, Run & Available Space Calculator
Enter the finished-floor rise, maximum target riser and tread depth to divide a straight flight into equal risers. Optionally compare the calculated run with your available horizontal space. The upper floor is assumed to be the final walking surface.
Enter your numbers
How this calculator works
Risers = total rise ÷ target riser, rounded up. Actual riser = total rise ÷ riser count. Treads are generally one fewer than risers for a typical floor-to-floor stair.
Worked example
Compare a 140-inch and 150-inch run with a diagram →
A 108 in rise with a 7.5 in target produces 15 risers at 7.2 in each, 14 treads, and a 140 in run.
Measure total rise from finished surface to finished surface
Total rise is the vertical distance between the lower finished floor and upper finished floor. Framing-only measurements can change after flooring is installed, creating uneven first or last risers. Measure the actual elevation difference and account for finish thickness before laying out the stringer.
The available horizontal run, headroom, landing size, nosing, handrail, and guard requirements also affect whether a stair fits safely.
Use the result as layout support
The calculator divides total rise into equal risers and estimates tread run. It does not determine code compliance or structural capacity. Verify locally applicable limits and mark a full-size story pole or test layout before cutting stringers.
Sources & assumptions
This is a geometry layout estimate, not a code-compliance determination. Verify riser consistency, tread depth, nosing, headroom, landings, guards, and handrails with the locally adopted building code.
Frequently asked questions
Why is the number of treads one less?
For a typical stair between floors, the upper floor acts as the final walking surface. Layouts with landings or other conditions can differ.
Does this confirm code compliance?
No. Verify maximum riser, minimum tread, headroom, handrail, landing, and consistency requirements with the governing code and inspector.
Stair layout guide
Follow the complete geometry example and code-check list in the Stair rise, run, and riser count guide.