Everyday
Stair Calculator
Enter the floor-to-floor rise to get riser height, tread count, total run, stringer length, and an IRC compliance check, with a side-elevation diagram. L and U shapes included.
How it works
Behind the numbers
Stair math starts from the total rise, the vertical distance between finished floors. Dividing by the maximum allowed riser (7¾ in under the IRC) and rounding up gives the riser count; the actual riser height is the total rise divided by that count, which keeps every step identical.
The top tread is the upper floor itself, so a 14-riser stair has 13 treads, and total run is 13 times the tread depth. Stringer length is the hypotenuse of rise and run. L and U shapes split the risers into two flights around a landing, which is how you fit a tall rise into a shorter footprint.
The compliance check tests your numbers against the International Residential Code: riser at most 7¾ in, tread at least 10 in, headroom at least 6 ft 8 in, width at least 36 in. Headroom is measured at the lower edge of the floor opening along the stair slope. Local amendments vary, so confirm with your building department before you build.
FAQ
Questions, answered
How many steps do I need for my stairs?
Divide the total floor-to-floor rise by the maximum riser height (7¾ in) and round up. A 105-inch rise needs 105 ÷ 7.75 = 13.5, rounded up to 14 risers, each exactly 7.5 in. Every riser in a flight must be uniform within ⅜ in.
What is the standard stair riser height and tread depth?
The International Residential Code allows a maximum riser of 7¾ inches and requires a minimum tread depth of 10 inches, with at least 36 inches of stair width and 6 ft 8 in of headroom. These are minimums for safety; many builders prefer a 7-inch riser with an 11-inch tread for comfort.
How do you calculate stair stringer length?
A stringer is the hypotenuse of the total rise and total run: √(rise² + run²). For a 105-inch rise and 143-inch run, the stringer is about 177.4 inches. Cut one as a template and test-fit it before cutting the rest.
Do I need a landing in my staircase?
The IRC requires a landing when a single flight rises more than 12 feet, and landings are also how L-shaped and U-shaped stairs change direction. A landing must be at least as deep as the stair is wide. This calculator flags any straight run over 12 ft of rise.