Stair layout calculator

Designing a stair picks riser and tread sizes. Laying it out means physically marking those numbers onto the framing so the stair lands exactly where it's supposed to.

You're usually working from a rough opening in the floor above, a header at the top, and a finished floor line at the bottom — none of which line up perfectly with the theoretical numbers until you account for floor thickness and finish materials.

The top riser height is measured from the top of the upper finished floor down to the top of the first tread below it — not to subfloor, unless your subfloor and finish floor are the same thickness as the lower level's.

If the upper floor has 3/4 in flooring the lower level doesn't have yet, that difference has to come out of the top riser or it'll be taller than the rest. Enter your floor thickness so the calculator adjusts for it.

Mark the top riser location on the header or rim joist first, since everything else — total run, stringer length, bottom landing point — is measured down and out from that mark.

Snap a chalk line from directly under the top riser mark out to the calculated total run distance. That line is your reference for stringer placement and for checking that the stair actually fits the available opening.

If the rough opening above is shorter than the total run below (common with steep stairwells), the diagram and layout numbers will show it immediately — you'll either need a steeper riser or a longer opening.

Headroom is the vertical clearance measured from the nosing line of each tread straight up to the framing or finished ceiling above. Commonly cited IRC reference values call for a minimum of 6 ft 8 in of headroom over the full stair, though local codes vary and the authority having jurisdiction makes the final call.

The rough opening length you enter determines where the header ends and open stairwell begins — walk that point on the diagram and confirm it clears the required headroom before you frame anything permanent.

A story pole is a straight board marked with each riser height, held plumb next to the framing to transfer riser marks without re-measuring every time. It's faster and less error-prone than pulling a tape for each of fifteen risers.

Mark your story pole using the exact riser height this calculator returns, not a rounded number — a 1/8 in rounding error repeated over fifteen risers adds up to almost 2 in of drift by the top.

1. Rip a straight, stable board to slightly longer than total rise.
2. Mark the finished floor line at the bottom.
3. Step off each riser height up the board with a compass or tick marks.
4. Label the top riser mark clearly — it's your reference for the header cut.
5. Use the pole to transfer marks to stringers or wall layout lines.

If the stair runs against a wall, skirt boards need a layout line parallel to the walking line, offset by the tread and riser thickness. Snap this line before installing stringers so the skirt sits tight without gaps at each step.

The side-elevation diagram gives you the exact rise-over-run slope to transfer to a level or laser for that line.