Calculate Every Stair Riser,
Code-Compliant & Safe.
Free stair calculators: rise and run layouts by the comfort rule and IRC limits, headroom checks before framing, stringer length and stock sizing, and runner lengths. No sign-up.
IRC Building Code Compliance
Ensures maximum 7-3/4" unit rise and minimum 10" run with consistent tread heights throughout.
Blondel Comfort Formula
2 × Rise + Run = 24 to 25 inches: the ergonomic human cadence standard for zero-trip climbing.
Stringer Cut Dimensions
Accounting for finish tread thickness when dropping the bottom stringer notch.
StairCalc Calculators
Stair Rise & Run Calculator
Equalized risers from total rise, tread by the comfort rule, with IRC limits checked.
Stair Headroom Calculator
The 80-inch check before the floor opening exists — required opening length from your layout.
Stringer Length & Stock Calculator
Slope length and board width from your layout — plus stringer count and span warnings.
Building Code & Methodology
Blondel's Formula: The 350-Year-Old Rule That Still Fits Your Legs
2R + T ≈ 25 inches — a 17th-century architect's comfort formula that modern codes still echo. Where it came from and how to use it.
Cut the Stringer Once: Template Discipline and the 3/8-Inch Rule
Stair codes measure uniformity before anything else. The template method that makes every stringer identical — and the errors it prevents.
The 80-Inch Line: How Stair Headroom Actually Fails
Headroom failures hide at the floor opening's edge. Where the check happens, why ducts eat the margin, and the framing-stage fixes.