Stair Stringer Calculator
Enter total rise and desired step size to get code-compliant riser/tread counts and exact stringer length.
About this tool
Get a Code-Compliant Stringer Layout Before You Cut a Single Board
Stringer math is unforgiving — every riser on a staircase has to come out the same height, or the whole thing feels wrong underfoot and can fail inspection. Rather than dividing your total rise by a guessed riser height and hoping it comes out clean, this calculator takes your total floor-to-floor rise and your target riser/tread size, then works backward to the nearest whole number of steps, tells you the actual riser height that results, and gives you the exact stringer length to cut — with a quick check against common US residential code limits.
How to use it
- Measure your total rise — the exact vertical distance from the finished floor at the bottom to the finished floor at the top — and enter it in inches.
- Enter your target riser height (7½" is a common comfortable default) and tread depth (10" is the typical code minimum for main stairs).
- The calculator rounds to the nearest whole number of risers and shows you the actual riser height that results — it usually won't be exactly what you typed, since the total rise has to divide evenly.
- Read off the stringer length, total run, and step count, and check the code note for any values outside common residential limits.
Real-world use cases
Framing a new deck staircase and needing the exact stringer cut length before buying lumber, replacing an existing interior staircase and wanting to double-check the riser count is code-compliant, planning a basement stair layout where floor-to-floor height is fixed and you need to know how many steps fit, or verifying a contractor's stair layout against your own numbers before construction starts.
Frequently asked questions
Why doesn't my actual riser height match what I typed in?
The total rise has to be divided evenly across a whole number of steps — you can't have a fraction of a riser. The calculator finds the number of risers that gets closest to your target height, then shows the actual height that results from dividing your exact total rise by that whole number.
What is the "17-18 inch rule" mentioned in the code note?
It's a widely used comfort guideline (not a strict code rule everywhere) stating that riser height plus tread depth should land between 17 and 18 inches. Stay in that range and stairs generally feel comfortable to climb — go much outside it and steps start to feel cramped or awkwardly stretched.
Why is the number of treads one less than the number of risers?
Every step up is a riser, including the very last one that brings you level with the upper floor — but that upper floor itself serves as the final "tread," so there's always one fewer physical tread board than there are risers.
Does this calculator account for stringer board thickness or notch depth?
No — this gives you the geometric stringer length (the hypotenuse of the total rise and total run), which is the number you need before laying out the actual step notches on a 2×12 or similar board. The physical notch layout and board width required depend on your specific riser/tread combination and are typically marked out directly on the lumber with a framing square.
What building code should I actually check?
Requirements vary by country, state, and sometimes by whether the stairs are for a main living space, a basement, or an exterior deck — the 7¾" max riser and 10" min tread used here reflect common IRC (International Residential Code) baseline figures for the US, but always confirm against your local building department before construction.