Ben built and runs stair-calculator.com. He has an academic background in civil and architectural engineering, and started the site after re-deriving the same stair math one too many times on scrap plywood. He writes the guides here and keeps the calculator's code checks aligned with the International Residential Code (IRC R311.7), cross-checking every figure and worked example against the published code text and standard carpentry references. The tool is deliberately free, with no sign-up and no paywall.

What I cover here

• How to calculate stair risers & number of steps — the formula, a worked example, and a floor-height reference table.
• How to calculate and cut stair stringers — stringer-length math, then framing-square layout to finished cuts.
• Stair building code requirements, explained — IRC R311.7 limits in plain English.
• The 2R + T rule — where the comfort formula comes from and how it meets code.

Accuracy & corrections

Every formula and code reference is verified against the published IRC text before it ships, and figures are reviewed on an ongoing basis (this profile and the guides carry review dates). Spotted an error in a formula or a code figure? Report it via the contact page — reported mistakes are fixed quickly and the change date is noted on the affected page.