Stair Calculator
Turn a total rise into a stair layout: riser count, actual riser height, tread count, the 2R+T comfort value, stringer length, and an optional two-flight landing. Everything runs in your browser.
How to use
- Measure the total rise from the finished floor below to the finished floor above, in inches. Flooring counts: measure to the top of the upstairs surface, not the subfloor.
- Enter the riser height you want and the tread run you have room for. The riser count rounds up, so the stair you build never has a riser taller than your target.
- Pick one straight flight, or two flights with a landing if the stair turns. The landing is laid out at least as deep as the stair is wide.
- Read the results: actual riser height, tread count, the 2R+T comfort value, stringer length, and total run. Cut one stringer first and test-fit it before cutting the rest.
How the math works
The riser count is your total rise divided by the target riser height, rounded up with the ceiling function, and the actual riser is the total rise split evenly across that count. Each flight's stringer length is the hypotenuse of its slope, the square root of run squared plus rise squared. All lengths are inches, and results are rounded to two decimals.
The 2R+T comfort value uses the actual riser, not the target, so it reflects the stair you would really build. Landing depth equals the stair width or the tread run, whichever is deeper. Headroom, nosing overhang, and handrail clearances are not modeled.
Stringers and treads are cutting jobs, not exact orders. Buy one more tread than the count suggests and keep about 10 percent spare stock for a bad cut or a twisted board.
Frequently asked questions
Are my measurements uploaded anywhere?
No. The calculator runs entirely in your browser tab, and your numbers never leave the page. Nothing is stored, nothing is sent to a server, and the page sets no cookies. Ad slots on the page are served by third-party networks, which follow their own privacy policies.
Why does the riser count round up?
Because a stair must climb the full rise in a whole number of equal steps. Dividing 108 inches by a 7.5 inch target gives 14.4 risers, and a stair cannot have 0.4 of a riser, so the calculator uses 15 and the actual riser comes out at 7.2 inches, at or below your target.
What is the 2R+T rule?
It is the classic stair comfort check: two riser heights plus one tread run should land between 24 and 25 inches. A 7.5 inch riser with a 10 inch tread scores 25, right in the band. The result shows your score and whether it falls inside that range, so you can trade riser height against tread run before you cut anything.
How does the landing layout work?
Choosing two flights splits the risers between them, with the first flight taking the extra one on an odd count, and the landing sits at the turn. The landing depth is set to your stair width or your tread run, whichever is deeper, and the total run adds the landing between the two flights. Headroom above the landing is not modeled, so check it separately on staircases that pass through a floor opening.
Does this guarantee a code-compliant stair?
No. It does the arithmetic. Building codes cap riser height and set minimum tread depth, headroom, and handrail rules, and the numbers differ by jurisdiction. Use the results to lay out a sane stair, then confirm the details against your local code before you build.