Stair Calculator
Work out the number of steps, riser height, run and stringer length.
Design a straight staircase: how many steps you need, the exact riser height, the horizontal run and the stringer (the diagonal board) length.
How the Math Works
The Stair Calculator uses fundamental division and rounding to determine stair dimensions. It begins by dividing the total vertical rise by a target riser height (typically 7-7.5 inches) and rounding to the nearest whole number to get the total risers needed. Then it recalculates the exact riser height by dividing the total rise by the rounded riser count, ensuring all steps are uniform height while meeting building code requirements. The run (tread depth) is typically set to a comfortable standard like 10-11 inches, and stringer length is calculated using the Pythagorean theorem: the square root of (riser height squared plus run squared), multiplied by the number of risers.
Practical Applications
To use this calculator practically, first measure the total vertical distance from your landing to your destination floor. Enter this measurement along with your desired riser height into the calculator. It will output the exact number of steps needed, the precise riser height for uniform steps, the recommended tread depth for comfort, and the required stringer length for cutting your support beams. This ensures your stair installation meets safety standards while using minimal materials efficiently.
Day-to-Day Use
This calculator transforms complex architectural math into everyday practicality, helping homeowners build safe, code-compliant stairs for decks, porches, basements, or loft conversions. Whether you're adding a backyard deck, finishing a basement, or building a home office, it eliminates guesswork and costly mistakes. Proper stair calculations prevent accidents, ensure comfortable climbing, and save time and money by providing exact cutting measurements for lumber, making DIY projects achievable for anyone with basic tools and measurements.
Worked example
105 in rise, 7 in target → 15 risers of 7.0 in, 14 treads × 10.5 = 147 in run, stringer = √(105² + 147²) = 180.7 in.
FAQ
What is a safe riser height?
Building codes commonly cap risers at ~7.75 in and require treads of at least ~10 in.