Stair Calculator

What a stair calculator is solving

Straight stair planning is a geometry problem. You usually know the total rise between finished floors and you have a preferred riser height and tread depth in mind. The calculator then shows how many risers are needed, what the actual riser height becomes once the count is rounded to a whole number, and how much horizontal run the stair will need.

That makes this kind of stair rise and run calculator useful early in design, renovation, and framing takeoffs. It helps you test whether a stair is likely to fit the available footprint before you move on to code checks, headroom, landings, nosings, and finished construction details.

Core stair formulas

The calculator uses straightforward layout maths. A target riser suggests the whole-number step count, the actual riser is recalculated from the full rise, and the total run follows from the tread count and chosen tread depth. Stringer length is then the hypotenuse of the rise-and-run triangle.

How to use the estimate on site

Start with the finished floor-to-floor rise, not the unfinished framing rise unless you are intentionally calculating from structural levels. Then enter a target riser and tread that reflect your preferred comfort and local code expectations. If the calculator produces an actual riser that is noticeably different from the target, adjust the inputs and compare the trade-off in total run.

For example, a rise of 2,700 mm with a target riser of 190 mm gives 14 risers. That yields an actual riser height of about 193 mm. If the tread depth is 250 mm, the stair needs 13 treads and about 3,250 mm of run. That quick check tells you whether the layout is plausible before detailed drafting.

What this result does not cover

This stair stringer calculator is a planning tool, not a code approval tool. It does not check local residential or commercial stair rules, landing requirements, handrail rules, nosing detail, finished-floor build-ups, or headroom. It also assumes one straight flight rather than winders, quarter turns, or split landings.

Use the result to compare layout options, then verify the final stair design against the code and construction standards that apply where the stair will actually be built.