Stair & Stringer Calculator
Plan a straight flight with equal risers. Find riser height, tread count, total run and stair pitch, with a scaled side-view diagram. The upper floor acts as the final landing.
How to calculate stair rise and run
Automatic riser count = total rise divided by your preferred maximum riser height, rounded up. Actual riser height = total rise divided by that count. With the upper floor serving as the last landing, tread count is one fewer than riser count. Total horizontal run = tread count × going.
Stair pitch = arctan(actual riser height ÷ going). The sloping line through corresponding tread points spans one fewer rise than the floor-to-floor height; its geometric length is tread count × √(riser² + going²). The separate floor-to-floor diagonal connects the bottom floor corner to the upper landing corner.
Is the stringer result a cutting length?
No. The tread-line span is a geometric reference, not a lumber cut list. End bearing, top attachment, tread thickness, bottom cut, stock depth, nosing and permitted notches affect a real stringer. Verify these details before cutting.
Can I use this for deck stairs?
Yes, for preliminary straight-flight dimensions. Measure between finished surfaces and enter the actual horizontal going, not the full tread board depth including its overhang.
Does this check building codes?
No. The preferred height is your input, not a legal maximum. This tool does not validate local requirements for headroom, landings, guards, handrails, loading or structural support. It does not design spiral stairs or turning landings.
Worked example
A 108-inch rise with a preferred maximum of 7.5 inches produces 15 risers of 7.2 inches. Fourteen 10-inch goings require 140 inches of horizontal space.
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