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StepCalc

Learn about staircases

The background behind the calculators — how stairs are designed, named and got wrong.

Two steps in section. The pitch line touches each nosing — headroom and pitch are both measured from it, not from the tread surface.treadnosingriser (the board)goingrisepitch line
Two steps in section. The pitch line touches each nosing — headroom and pitch are both measured from it, not from the tread surface.

Every page below is illustrated — the mistakes page draws each error as it actually looks on site.

How StepCalc calculates

Every number the calculators and the project planner produce — riser count, going, run, pitch, code checks, stringer cuts, the floor opening, balusters and the cut list — worked through on one real stair.

Area and perimeter, explained

What each formula means and where it comes from — rectangles to ellipses — plus square-unit conversions and how to handle irregular shapes.

Anatomy of a staircase

Every part named and explained, with US and UK terms side by side — because going and run are not quite the same thing and the difference causes real errors.

Eight mistakes that cost the most

Finished floors, the stringer drop, tread count, winder walk lines, accumulated rounding. The list that will save you a rebuilt flight.

The trigonometry of a staircase

A stair is a stack of identical right triangles. Angle from arctan, stringer from Pythagoras, floor opening from tangent rearranged — with a worked example.

The rules of thumb, and where they came from

Blondel's 1675 formula and the three that followed it — what each says, why they disagree, and which to trust.

Stair codes compared

IRC, IBC and UK Part K side by side, and an explanation of why three codes give three different answers.

Glossary

Every term defined, cross-referenced, US and UK.