A stair stringer calculator helps you build stairs by figuring out how many steps you need, the height of each riser, the depth of each tread and the length of the stringer board. Enter the total rise (the height from floor to floor or deck) and your preferred tread depth, and it does the layout math.
Start by dividing the total rise by a target riser height, often around 7 to 7.5 inches. For a 42-inch deck, 42 ÷ 7 = 6 risers of exactly 7 inches. The number of treads is usually one less than the number of risers when the top step is the deck itself, so you’d have 5 treads. With 10.5-inch treads, the total run is 52.5 inches. The stringer length is the hypotenuse: √(42² + 52.5²) ≈ 67.2 inches, so buy a board long enough with room for cuts.
Safety and code: building codes set limits on maximum riser height, minimum tread depth and how much risers can vary from one step to the next. In many US jurisdictions, residential stairs follow rules based on the International Residential Code, but local codes can differ, so check with your building department before you build.
Tips: use a framing square with stair gauges to mark cuts, account for the thickness of tread boards, and cut one stringer first and test it before cutting the rest. Use pressure-treated lumber for outdoor stairs and add handrails where required.
Tips for getting accurate results from the Stair Stringer Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
How to use the Stair Stringer Calculator on Minedit: enter your values in the fields, press calculate, and review the step-by-step breakdown under the result. If something looks off, change one input at a time to see how it affects the answer, which is also a great way to learn the math behind it.
Learn more about stairs on Wikipedia’s stairs article. Find rafter, stud and board feet calculators on Minedit.