How to use the stair stringer calculator
- Measure finished floor to finished floor, accounting for the intended finish layers.
- Choose a target riser and tread going appropriate to the design you are planning.
- Use the equal-rise result for preliminary layout, then verify applicable requirements and the physical stringer details.
The formula
Risers = ceiling(total rise ÷ target riser); actual riser = total rise ÷ risers; run = (risers − 1) × going
Worked example
A 108 in total rise with a 7.5 in target produces 15 risers at 7.2 in each. Fourteen 10 in goings create a 140 in total run.
Before you measure and cut
This model treats the upper floor as the final landing, so there is one fewer tread than risers.
The diagonal is a geometric reference, not a lumber cut length. Top and bottom attachment, tread thickness, and end cuts change the stock required.
Frequently asked questions
Does this confirm the stairs are legal?
No. Requirements depend on the location and application. This calculator intentionally does not encode a building code.
Why is tread count one less than riser count?
The upper floor serves as the last landing. A different landing arrangement requires a different model.