Stair calculator with diagram

A calculator can tell you riser height is 7.2 in and tread depth is 10.5 in and everything can still look correct on paper while being wrong on the wall.

The drawing shows how those numbers stack against the actual opening — the header, the floor thickness above, the wall the stringer lands against. A number sheet won't show you that the top riser is 3/8 in taller than the rest because nobody accounted for finish flooring.

Framers who skip the drawing and work from a number list are the ones who cut fourteen stringers before noticing the run is six inches longer than the stairwell.

The side-elevation is the profile view you'd see standing at the bottom of the stair looking at it from the side. It shows the full rise as a vertical line on the left, the full run as a horizontal line along the bottom, and each step as a small zigzag between them.

Every riser line is vertical, every tread line is horizontal, and the diagonal line connecting the nosings is the walking line — roughly where your foot lands as you climb.

The nosing line is drawn slightly forward of the riser face on closed-riser stairs, usually by about 1 in, and this calculator's default reflects that so the drawing matches a typical residential tread overhang.

• Vertical segments = riser faces, each labeled with height
• Horizontal segments = tread runs, each labeled with depth
• Dashed diagonal = the nosing line, useful for checking headroom clearance
• Total rise and total run are labeled at the outer edges

The stringer diagram is the cutting pattern — the sawtooth shape you'd actually mark on a 2x12 with a framing square. It shows the same riser and tread dimensions as the side-elevation, but oriented as a single board outline instead of a stacked profile.

Plumb cuts (the vertical faces you cut against the riser) and level cuts (the horizontal faces you cut for the tread to sit on) are the two cut types every notch needs, and the diagram distinguishes them so you don't confuse the framing square angle.

The bottom of the diagram shows the drop — how much material is trimmed off the first cut so the bottom riser matches the others once the stringer sits on the finished floor.

Once the numbers look right, print the diagram and take it to the site instead of re-typing values into a phone with cold hands and sawdust everywhere.

A printed side-elevation taped inside the stairwell lets a second carpenter frame the header and rough opening from the same drawing you used to cut stringers, which keeps the whole crew working from one source of truth.

1. Measure total finished rise (subfloor to subfloor, or slab to finished floor) and enter it.
2. Enter your target riser height — 7.25 in is a common residential starting point.
3. Check the riser and tread the calculator returns; adjust nosing if your tread stock has a different overhang.
4. Review the side-elevation for headroom and the stringer diagram for cut angles.
5. Print or screenshot both diagrams before you start cutting.

The most common one is a mismatched top riser: if the finished floor thickness at the top isn't subtracted from total rise before you run the numbers, the diagram will show a top step that's visibly taller than the rest.

The second is forgetting the stringer drop. Without dropping the bottom of the stringer by one riser thickness, the diagram (and the real stair) ends up one full riser too tall.

A diagram also flags an impossible run early — if your available floor space is 10 ft but the drawn total run is 12 ft 3 in, you'll see the overhang before you've cut a single board.

A flat side-elevation is enough for a straight run, but if you're picturing an open-riser stair, a stair with a landing, or how treads will look against an existing wall, a visual or rendered view helps clients understand the design faster than a dimension table.

For turned stairs, use the L-shaped or U-shaped stair calculator on this site, which draws the landing and both flights so you can see how the turn actually lines up.