Stair Calculator
Design stairs that pass inspection: enter your total rise and get riser count, tread layout, total run, and stringer length — with code-limit checks built in. Runs 100% in your browser.
Stair Calculator
About this stair calculator
Stair math is one division and one rule: divide your total rise by a target riser height, round up to whole risers, then divide again for the actual riser height. This calculator does that, then lays out the treads, total run, and stringer length — and flags anything outside common residential code limits (7 3/4 in max riser, 10 in min tread, handrails at 4+ risers).
A comfortable stair lands around a 7–7.5 in riser with a 10–11 in tread, giving a 32–37° angle. The classic rule of thumb: riser + tread should total roughly 17–18 in. Steeper than that feels like a ladder; shallower eats floor space for no comfort gain.
The stringer length is the diagonal from top to bottom — rise² + run², square-rooted. Buy stringer stock longer than the number (a 2×12 for cut stringers), and remember cut stringers need at least 5 in of solid wood below the notches. Always confirm with your local building department — codes amend these numbers.
How to use
- Measure the total rise in inches — floor to floor, or deck surface straight down to the ground.
- Enter your target riser height (7.5 in is a comfortable default) and tread depth (10 in minimum).
- Press Calculate for riser count, actual riser height, treads, total run, and stringer length.
- Check the code notes, then confirm with your local building department before cutting.
Good to know
- Straight runs only — L-shaped, U-shaped, and winder stairs need landing and turn math this tool does not do.
- Code checks reflect common US residential (IRC) limits; local amendments vary — verify before building.
- This is a layout tool, not structural or code advice. Stringer spacing, attachment, and guards must follow local code.
Frequently asked questions
How many steps do I need for a 4 foot high deck?
A 48 in rise divided by a 7.5 in target riser gives 7 risers (6.86 in each) and 6 treads. More generally: risers = total rise ÷ target riser, rounded up; treads = risers − 1.
What is the standard stair riser height?
Residential code caps risers at 7 3/4 in; 7–7.5 in is the comfortable range. All risers in one flight must be uniform within 3/8 in.
What is the standard tread depth?
10 in minimum measured nosing to nosing in residential code; 10–11 in is comfortable. Deeper treads suit exterior stairs.
How do I calculate stringer length?
Square the total rise, square the total run, add them, and take the square root — that diagonal is your stringer length. Buy stock longer than the result.
Do my stairs need a handrail?
In most residential codes, any flight with 4 or more risers needs a handrail at 34–38 in above the nosing line, on at least one side.