Stair Calculator

The Stair Calculator plans a straight staircase from the total rise between two finished floors. Set a target riser height or a fixed number of risers, then let the tread depth follow the 2R + T comfort rule, fit the stair into the run you have, or enter a fixed tread. You get the exact riser height, tread depth, tread board size with nosing, total run, pitch angle, stringer length and headroom, along with a side-view drawing of the stair and the floor opening.

Every design is checked against a set of rules: general comfort guidance, the IRC for US homes, DIN 18065 for German residential buildings or Approved Document K for a private stair in the UK. The checks cover riser height, going, the step-length rule, pitch, headroom, stair width, risers or rise per flight, nosing where the IRC requires it, and how much wood remains below the notches of the stringer board.

The stair calculator helps DIY builders laying out deck, basement or loft stairs, carpenters cutting stringers, and homeowners checking whether an existing staircase is comfortable. Local rules and amendments vary, so confirm the final design with your building authority before cutting.