ABC Tools
Stair Calculator illustration

Stair Calculator

Divides a floor-to-floor rise into equal risers, checks the classic 2R + T comfort rule and common code-style limits, computes the total run, stair angle and stringer length, and shows nearby alternatives with one or two risers more or fewer so you can trade steepness against run.

Read the full guide to this tool

Finished floor to finished floor, including the upper floor thickness.
Leave blank if the run is unconstrained.
Comfortable stairs use 150–190 mm risers.
Used for the stringer drop: the bottom of the stringer is cut down by one tread thickness.
Horizontal depth per step, nosing excluded; 250–300 mm is typical indoors.
Vertical clearance over the stair; most codes want about 2000 mm or more.

Notes

  • Blondel's rule: twice the riser plus the tread (2R + T) should land between 600 and 660 mm — the length of a natural step.
  • Riser limits differ by country; around 190 mm is a common maximum for private stairs. Always check your local building code.
  • All risers must be equal — a single odd riser is a classic trip hazard, which is why the calculator divides the exact rise instead of using the target directly.

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