Start with the shape of the stair and the space available. Pro² for iPhone has separate tools for a straight flight, a quarter turn, a half turn and a spiral.
Floor-to-floor height; three flight lengths and widths; turn direction; turning arrangement and top-tread position. The gap follows from the middle-flight dimensions.
What you get
A three-flight plan, riser height, going and pitch for each flight, and tread details.
Schematic plan · not to scale
Spiral stairs
Around a central axis
Treads turn around an inner radius. Their depth changes across the width, so a straight-stair formula is not enough.
Total rise; target riser height; inner radius; radial tread width; total rotation.
What you get
Riser and tread counts, step angle, arcs and chords, inner and outer stringer pitches and cumulative marks.
What to measure before you calculate
Record the floor-to-floor height, the available opening and the direction of travel at the top. For turning stairs, measure the footprint of each flight. For a spiral, keep radius and diameter distinct.
Measure between finished floor levels.
Note where the stair enters and leaves the opening.
Keep measurements in a consistent unit system.
Work out your stair dimensions.
Use your own measurements for stair geometry and baluster spacing in Pro² for iPhone.
